Roman Geographers and Their Contributions: Strabo, Mela, Pliny and Ptolemy

Roman Geographers: Meaning, Scope and Place in Geographical Thought

Roman Geographers and the Oikoumene

The Roman geographers set out to describe or map the oikoumene, the inhabited world as the ancients knew it. For them it ran from the Atlantic coast of Europe and Africa in the west to China in the far east, and it was only a part of the globe. Ptolemy himself knew that the known world was only about a quarter of the Earth.

The group is not uniform. Pomponius Mela, a native of southern Spain who wrote around AD 43, and Pliny the Elder (AD 23 or 24 to 79) wrote in Latin. Strabo (about 64 BC to AD 24) came from Amaseia in Pontus and wrote in Greek. Marinus of Tyre (about AD 70 to 130) was a Greek-speaking Phoenician from the Roman province of Phoenicia. Ptolemy (about AD 100 to the 160s or 170s) lived in or near Alexandria in Roman Egypt and wrote in Greek.

What unites them is the setting. Their sources, patrons and readers belonged to the Roman world, and the roads, sea routes and trade of that world supplied their information.

Roman Geographers in the History of Geographical Thought

In the history of geographical thought the Roman period matters in three ways. It preserves Greek geography, because the works of almost all earlier geographers are lost and many are known only from quotations in Strabo. It adds new knowledge, because the expanding empire brought the British Isles into the picture and the Silk Road brought the far east into view for the first time. And it hands the subject on, because Ptolemy's coordinates and Strabo's regional descriptions reached the Arabs and then Renaissance Europe.

In the evolution of geographical thought, a topic of Geography Optional Paper I, the Roman geographers therefore stand between the Greek founders and the Arab and Renaissance inheritors. Beside this scholarly line stands a practical Roman contribution in roads, surveys and itineraries.

Greek Foundations That Roman Geographers Inherited

Eratosthenes: Geography, Circumference and the First Grid

Eratosthenes of Cyrene (about 276 to 194 BC), chief librarian at the Library of Alexandria, coined the words geography and geographer, from the Greek geo (earth) and graphos (description). He was the first known person to calculate the Earth's circumference, around 250 BC, and he made the first global projection of the world with parallels and meridians.

His measurement used two cities on nearly the same meridian, Syene (modern Aswan) and Alexandria. At noon on the summer solstice the Sun's rays shone straight down a well at Syene, while a vertical rod at Alexandria still cast a shadow. The shadow's angle was about 7.2 degrees, which is one fiftieth of a full circle. With the distance between the cities reported as about 5,000 stadia, he multiplied by 50 and reached roughly 2,50,000 stadia for the whole Earth.

The figure usually quoted for his result is 2,52,000 stadia, and one modern conversion puts it at about 40,338 km against a true equatorial circumference of about 40,075 km. He assumed that Syene lay on the Tropic of Cancer and due south of Alexandria. In fact Syene lies about 1 degree north of the Tropic and about 3 degrees east of Alexandria, but the two errors happened to cancel each other.

Spherical Earth, Climatic Zones and Three Continents

The Greeks established that the Earth is a sphere before any Roman geographer wrote. Pythagoras was perhaps the first to propose it, arguing that the sphere is the most perfect form. Plato accepted the idea and Aristotle supplied evidence from observation. He noted that the Earth's shadow on the Moon during a lunar eclipse is always curved, and that stars rise higher in the sky as an observer moves north. The Greeks also divided the globe into five zones, a cold region at each pole, a hot band around the equator, and a temperate belt in each hemisphere.

They divided the known land into three continents, Europe, Asia and Libya (Africa), and believed that a narrow habitable band ran from the Atlantic Ocean to an unknown sea east of India. These ideas pass directly into Roman writing. Mela repeats the five zones, and Strabo accepts the narrow band.

Hipparchus and Posidonius: Rigour in Position and a Smaller Earth

Hipparchus (about 190 to 120 BC) was a Greek astronomer and geographer. He wrote a three-book critique, Against the Geography of Eratosthenes, which survives only through Strabo. He insisted that a geographic map must rest only on astronomical measurements of latitude and longitude and on triangulation for unknown distances. He is credited as the first to apply mathematical rigour to fixing the latitude and longitude of places.

Posidonius (about 135 to 51 BC) measured the Earth by the star Canopus, which he saw just touch the horizon at Rhodes and rise 7.5 degrees at Alexandria. Taking 5,000 stadia between the two places and one forty-eighth of a circle, he multiplied by 48 and got 2,40,000 stadia. Strabo, however, gives the distance from Rhodes to Alexandria as 3,750 stadia, which with the same one forty-eighth gives 1,80,000, and he reports 1,80,000 stadia as Posidonius's estimate. The different lengths of Greek and Roman stadia have left his true result in doubt. The doubt matters because the smaller figure became the base of Ptolemy's map.

Two Traditions Inherited from Greece

Greek and Roman geographers shared one inheritance that split into two traditions. One tradition was descriptive. Hecataeus of Miletus avoided mathematical calculation and wrote a prose account of the world by gathering earlier works and questioning the sailors who passed through the port of Miletus. The other was mathematical. Eratosthenes, Hipparchus and Posidonius tried to measure the Earth and to fix places by astronomical observation.

Roman-era writers chose between these paths and sometimes combined them. Strabo took the descriptive path, and Ptolemy took the opposite course and built his work on coordinates. Pliny and Mela stood nearer to the descriptive side, with Pliny collecting information from other authors and Mela describing the world coast by coast. This split between description and measurement is the main thread that runs through Roman geography.

Strabo's Geographica: Descriptive and Regional Geography

Strabo: Life, Travels and Dates

Strabo was born about 64 BC into a wealthy family at Amaseia in Pontus, in Asia Minor, and died about AD 24. He moved to Rome in 44 BC and stayed at least until 31 BC. His teachers included Tyrannion, a respected authority on geography, the Peripatetic Xenarchus and the Stoic Athenodorus. His earlier teacher Aristodemus had been the grandson of Posidonius, whose influence shows in the Geographica.

Travel supplied much of his evidence. He went to Egypt and sailed up the Nile as far as Philae around 25 BC, and he ranged from Tuscany in the west to the borders of Ethiopia in the south. He wrote that perhaps no author of a geography had visited more places between those limits. He also spent time at the Library of Alexandria taking notes from the works of his predecessors.

The exact date of his Geographica is unsettled. A first edition may belong to about 7 BC, and the finished work belongs to the reign of the emperor Tiberius. The latest event he mentions is the death of the Mauretanian king Juba II in AD 23.

The Geographica: 17 Books and the Descriptive Method

The Geographica is an encyclopaedia of geographical knowledge in 17 books, written in Greek. It is almost completely preserved, which is why it is one of the most important sources for classical geography, and it is the only surviving work that describes both Greek and Roman peoples and countries in the reign of Augustus.

Strabo cited the astronomers Eratosthenes and Hipparchus but claimed that a descriptive approach was more practical. He wrote for statesmen interested in the character of countries and regions rather than in numbers, and he proposed to omit what is petty and to dwell on what is great, useful or memorable. His last book describes Alexandria as a thriving port with streets wide enough for chariots and horsemen. He dismissed the voyages of Hanno and Pytheas as fables. None of his maps survives, but his descriptions show what the educated Roman world knew.

Strabo on Coasts, Land Movement and Rivers

Strabo defined geography through the coastline. It is the sea above all, he wrote, that gives the land its shape by forming gulfs, straits, isthmuses, peninsulas and promontories, while rivers and mountains assist. From these natural features a reader gains a clear idea of continents, nations and the positions of cities.

He also reasoned about change in the Earth. Discussing marine shells found far from the sea, he argued that the same land is sometimes raised and sometimes depressed, and that the sea moves with it, an idea that the geologist Charles Lyell later admired. He recorded volcanic soils at Katakekaumene in western Turkey, arguing that the ground had been burned by a fire from underground whose source had died out. And in Europe he was the first known writer to state that the Danouios and the Istros were the upper and lower parts of one river, the Danube.

What Strabo Recorded about India and Taprobane

Strabo never visited India, and his account mixes fact with fable. He described small flying reptiles with snake-like bodies and bat-like wings, a description that matches the Indian flying lizard, but he also wrote of winged scorpions. He noted that Taprobane, the Greek name for Sri Lanka, sent great amounts of ivory, tortoise-shell and other merchandise to the markets of India.

His most useful Indian evidence concerns trade. While travelling up the Nile with Gallus, the prefect of Egypt, he learned that as many as 120 vessels were sailing from Myos Hormos on the Red Sea to India. Under the Ptolemies, he observed, only a very few had dared to make the voyage. The vast increase in trade that he reports followed the Roman annexation of Egypt, and it shows that the monsoon was known in his time.

Pomponius Mela's De situ orbis: The First Latin Geography

Mela: Life and Date of the Work

Pomponius Mela was born at the end of the first century BC at Tingentera in southern Spain, on Algeciras Bay, and died about AD 45. Little else is known of him. His date of writing is fixed by his reference to a proposed British expedition of the reigning emperor, almost certainly the expedition of Claudius in AD 43.

His short work, De situ orbis, in three books, takes up less than a hundred pages of ordinary print, yet it remained in use almost until the year 1500. Apart from the geographical parts of Pliny's Natural History, where Mela is cited as an important authority, it is the only formal treatise on geography in classical Latin. Its first printed edition appeared at Milan in 1471.

Mela's Five Zones, Antichthones and Coastal Tour

Mela's general views follow the Greek writers from Eratosthenes to Strabo, although Strabo was probably unknown to him. He divided the Earth into five zones, of which only two were habitable. He is unique among ancient geographers in asserting that there are antichthones, people living in the southern temperate zone, cut off from the northern temperate peoples by the unbearable heat of the torrid zone between them.

His method is a coastal tour in the manner of a periplus, a sailing guide that records the coasts, ports and distances met on a voyage. It probably came from navigators' accounts. He begins at the Straits of Gibraltar, follows the south coast of the Mediterranean, goes round Syria and Asia Minor to the Black Sea, and returns to Spain along its northern shore. He then takes the ocean coast from Spain and Gaul round to India, from India to Persia, Arabia and Ethiopia, and back to Spain.

Mela's Strengths and Inherited Errors

Mela knew western Europe better than the Greeks did. He defined the western coast of Spain and Gaul and the indentation of the Bay of Biscay more accurately than Eratosthenes or Strabo, and he was the first to name the Orkney Islands, which he located fairly correctly. He also mentions a great bay north of Germany, with an island, which reappears in Pliny as Scatinavia.

Elsewhere he repeated old errors. Like every classical geographer from the time of Alexander the Great except Ptolemy, he treated the Caspian Sea as an inlet of the Northern Ocean. He followed Eratosthenes in placing India in the south-eastern corner of Asia, and his picture of India is poorer than that of some earlier Greek writers. Africa, for him, was a continent surrounded by sea that did not extend very far south.

Pliny the Elder's Natural History and Its Geography

Pliny the Elder: Life and the 37-Book Natural History

Pliny the Elder (AD 23 or 24 to 79) was a Roman author, naturalist, scientist and naval and army commander who served the emperor Vespasian. His birth year is inferred from his nephew's statement that he died in his 56th year, and his death date is fixed by the eruption of Mount Vesuvius in AD 79. As admiral of the fleet at Misenum he sailed across the Bay of Naples to rescue a friend at Stabiae and died there.

Of seven works in 102 volumes, only the Natural History survives. Its dedication to the future emperor Titus points to about AD 77, and Pliny was still revising it when he died.

The Natural History is the largest single work to survive from the Roman Empire. Its 37 books cover astronomy, mathematics, geography, ethnography, zoology, botany, agriculture, mineralogy, art and precious stones. Pliny gathered his information from other ancient authors and named them, and his list of contents and his habit of citing original authors made the work a model for later encyclopaedias.

Books 3 to 6 describe the known world region by region.

1. Book 3: The Iberian peninsula and Italy.
2. Book 4: Europe.
3. Book 5: Africa and Asia.
4. Book 6: The Black Sea, India and the Far East.

Pliny is a compiler more than an observer, and he and Strabo were generally slow to use the reports of merchants and sailors. His value lies in what he preserves, since 16 fragments of Eratosthenes's Geographica survive in his pages.

Pliny on India, the Monsoon and the Drain of Gold

Pliny's best-known remark on India is an economic one. He complained that India, China and the Arabian peninsula together took a hundred million sesterces a year from the Roman Empire, at a conservative estimate, in payment for luxuries. The remark makes the Natural History a Roman witness to the scale of eastern trade, in which Roman gold and silver flowed out to pay for goods such as silk.

Pliny also wrote on the monsoon route. The Periplus of the Erythraean Sea, a first-century sailing guide, credits a Greek navigator, Hippalus, with discovering the direct sea route across the open ocean from the Red Sea to India. Pliny said instead that Hippalus was the name of the south-west monsoon wind. Historians usually reconcile the two by saying that knowledge of the winds was needed to use the direct route.

Ptolemy and Mathematical Geography

Claudius Ptolemy: Life and Two Great Works

Claudius Ptolemy was a Greco-Roman mathematician, astronomer and geographer who lived in or near Alexandria in Roman Egypt, from about AD 100 to the 160s or 170s. His year of death is not recorded and is inferred from his output. He wrote about a dozen scientific treatises, and two of them shaped geography.

The Almagest, originally titled the Mathematical Treatise, is a 13-book work on the motions of the stars and planets, written possibly around AD 150. Its name comes from an Arabic corruption of the Greek for greatest, and its geocentric model dominated astronomy for more than 1,200 years. It also contains a star catalogue of 1,022 stars with ecliptic longitude and latitude. The second work is the Geography, written in Greek at Alexandria around AD 150.

The two books are linked, because Ptolemy argued that geography should rest on astronomical observation rather than on travellers' stories.

Marinus of Tyre: The Predecessor Behind Ptolemy's Geography

Marinus of Tyre (about AD 70 to 130) took the principle Hipparchus had set out, that places must be fixed by latitude and longitude, and applied it to a map of the whole known world. For this he is called the founder of mathematical geography, and Ptolemy used his work as the main source of the Geography. His own treatise is lost, so it is known only through Ptolemy's long discussion of it.

Marinus collected astronomically determined latitudes, lists of cities on the same meridian or parallel, coastal descriptions, provincial boundaries and the reports of traders and military expeditions. He devised a system of latitude and longitude with a zero meridian through the Fortunate Isles (the Isles of the Blessed), around the Canary Islands, and drew his map on an equirectangular projection whose standard parallel was that of Rhodes at 36 degrees north. He estimated the equator at 1,80,000 stadia, which corresponds to about 33,300 km, roughly 17 per cent less than the true value. He placed the habitable world from Thule at 63 degrees north to Agisymba at 24 degrees south, and from the Fortunate Isles to Sera (China) at 225 degrees east.

His maps were the first in the Roman Empire to show China. Ptolemy praised his improvements but found that Marinus had made Asia too long from west to east and Africa too long from north to south, and he corrected both.

Ptolemy's Geography: Eight Books, Gazetteer and Atlas

Ptolemy's Geography is at once a gazetteer, an atlas and a treatise on cartography. It revised the lost atlas of Marinus of Tyre, using additional Roman and Persian gazetteers and new principles. Its eight books are arranged as follows.

1. Book 1: A treatise on cartography, explaining how to assemble data, why astronomical observations take precedence over travellers' reports, and how to draw a world map.
2. Books 2 to 7: A gazetteer of some 8,000 place names, each placed by latitude and longitude, with Book 7 covering India, China and Sri Lanka.
3. End of Book 7: Three projections for drawing the world map, differing in complexity and fidelity.
4. Book 8: An atlas of regional maps. The standard Western set had 26 maps, 10 of Europe, 4 of Africa and 12 of Asia.

The original Greek manuscripts have not survived from before the thirteenth century, and it is uncertain whether the maps existed in antiquity. The surviving maps were redrawn from his coordinates, which shows how completely he had encoded the map in words and numbers. One of his methods outlived him. The equidistant (simple) conic projection, still used in atlases for regions in the middle latitudes, has its prototype in Ptolemy's work of about AD 150.

Latitude, Longitude and Map Projections

Ptolemy expressed latitude in degrees of arc from the equator, the system used today, though he used fractions of a degree where we use minutes. His prime meridian, the line of zero longitude, ran through the Fortunate Isles, the westernmost land he recorded, at about the position of El Hierro in the Canary Islands. His maps spanned 180 degrees of longitude from there to China.

His rule of method was to give priority to astronomical observations over records of travel. In practice he relied on Marinus, on gazetteers of the Roman and ancient Persian empires, and on Hipparchus for the elevation of the north celestial pole at a few cities. A framework so sound in principle therefore carried large errors in detail, because most places had never been fixed by observation.

Ptolemy's Errors: Earth Size, Stretched Longitudes and the Enclosed Indian Ocean

Ptolemy's grid was a leap forward, but his numbers carried errors that shaped European maps for centuries.

• Too small an Earth: Instead of the 2,52,000 stadia of Eratosthenes, he used 1,80,000 stadia, at 500 stadia to a degree. Strabo reports the same lower figure for Posidonius, and Marinus had used it before Ptolemy.
• Stretched longitudes: In a sample of 80 well-known cities from his gazetteer, longitude is overstated by a factor of about 1.428, which visibly stretches the shape of Italy sideways.
• An enclosed Indian Ocean: Relying on Hipparchus, he enclosed the Indian Ocean with an unknown land to the east and south, making it an inland sea like the Mediterranean. Eratosthenes and Strabo had treated it as part of the single World Ocean.
• A misread coast: A scribal error placed the port of Cattigara at 8.5 degrees south instead of north of the equator, so the coast of China came to look like an eastern shore of the Indian Ocean.

Ptolemy was also right where his predecessors were wrong. He described the Caspian Sea as an inner sea, a large lake, while Eratosthenes, Strabo and Mela had called it an inlet of the Northern Ocean.

Ptolemy's Map: India, Sri Lanka and the Great Gulf

Book 7 of the Geography covers India, China and Sri Lanka, and the world map built from it shows how the Roman world pictured South and East Asia. India is bounded by the Indus and the Ganges rivers, but its peninsula is much shortened. Sri Lanka, written Taprobane, is greatly enlarged. The Malay Peninsula appears as the Golden Chersonese, beyond which a Great Gulf, the Magnus Sinus, combines the Gulf of Thailand and the South China Sea. China is divided into two realms, the Sinae and the Land of Silk (Serica), because the overland and the maritime Silk Roads gave different accounts.

The gulf and the coasts east of India came from sailors. Marinus and Ptolemy relied on the testimony of a Greek sailor named Alexandros, who claimed to have visited Cattigara, most likely Oc Eo in Vietnam, where Antonine-period Roman goods have been unearthed. Where Strabo and Pliny were slow to use merchants' reports, Ptolemy was open to them, and the Bay of Bengal could not have been charted so well without traders.

Roman Practical Geography: Roads, Surveyors and Maps

Roman Roads and Milestones

The Romans made far more extensive practical use of geography and maps than the Greeks did. At the peak of Rome's development no fewer than 29 great military highways radiated from the capital, and the empire's 113 provinces were connected by 372 great roads. The whole network ran to more than 4,00,000 km, of which over 80,500 km were stone-paved. Roman road building began in the late fourth century BC, and the Via Appia from Rome towards Apulia dates to 312 BC.

Milestones turned the roads into measured geography. The modern word mile comes from the Latin milia passuum, a thousand paces, each pace being five Roman feet, so a Roman mile measured about 1,476 m. The Via Appia was divided into numbered miles even before 250 BC, and most roads were marked after 124 BC.

Alongside the roads stood the cursus publicus, the state courier and transport service created by Augustus to carry messages, officials and tax revenue between the provinces and Italy.

Gromatici, the Groma and Centuriation

The cursus publicus employed full-time surveyors, called gromatici, to gather topographical information and find the straightest possible route for a road. Their tool, the groma, projected right angles and straight lines. It is the only Roman surveying instrument of which examples survive, and it let surveyors set up rectangular grids.

The grid system was centuriation, a method of land survey in which a regular square grid of roads, canals and plots was traced across the countryside. Rome began using it in the fourth century BC in new colonies, and its standard form developed with the Po Valley colonies, beginning with Ariminum (Rimini) in 268 BC. It spread after the agrarian law of Tiberius Gracchus in 133 BC and was used to settle army veterans. Careful analysis has identified 80 different centuriation systems between Rome and Salerno alone.

Surveying work in the Greco-Roman world fell into four kinds.

• Land surveyors: Fixed field dimensions, divided land into plots and laid out town streets.
• Cartographical surveyors: Made maps, finding latitudes, longitudes and heights.
• Military surveyors: Measured, for example, the width of a river that an army must cross.
• Engineering surveyors: Prepared the ground for roads, canals, aqueducts, tunnels and mines.

Itineraries, Agrippa's Map and the Tabula Peutingeriana

Roman travellers relied on itineraries, lists of stations and distances along roads. The Antonine Itinerary is a register of stations and distances along the roads of the empire, seemingly based on official documents and possibly in part on a survey carried out under Augustus. All its surviving editions seem to trace to an original from near the end of the reign of Diocletian in the early fourth century.

Behind the itineraries stands the world map prepared under the general and statesman Marcus Vipsanius Agrippa in the reign of Augustus, which was engraved in stone and displayed in the Porticus Vipsania in Rome. The Tabula Peutingeriana, or Peutinger Table, is thought to descend from it. The surviving map is a parchment copy of about the year 1200 of a Late Antique original, assembled from 11 sections into a scroll 6.75 m long and 0.35 m high. It names no fewer than 555 cities and 3,500 other places and gives special icons to Rome, Constantinople and Antioch.

The Peutinger Table is a schematic map, like a modern transit diagram, designed to show the road network and not the true shape of land, so land masses are distorted east to west. It reaches India and the Ganges, shows Sri Lanka as Insula Taprobane, and marks a Temple of Augustus at Muziris on the Malabar coast. UNESCO added it to the Memory of the World International Register in 2007. Konrad Peutinger of Augsburg, who received it in 1508, gave it his name, and it has been kept in Vienna since 1738.

Roman Geographers and India

How the Roman World Recorded India

Roman-era writers knew India mainly through trade, and each of the four geographers whose works survive adds something to the Indian picture. Strabo supplies fable and a trade figure, Mela places India at the south-eastern corner of Asia, Pliny records the drain of money, and Ptolemy gives the most detailed Roman map of the subcontinent in Book 7.

Two things changed over time. The monsoon route opened a direct sea link, so ships no longer had to hug the coast. And knowledge of India's shape improved. Before Hippalus, Greek geographers thought the Indian coast ran from west to east. Hippalus was probably the first in the West to recognise that India's west coast runs north to south, and only someone with that insight would think that crossing the Arabian Sea might be a faster way to south India than following the coastline.

The Periplus, the Monsoon Route and the Ports of India

The Periplus of the Erythraean Sea was written in Greek in the first century by an anonymous Greek-speaking merchant of Roman Egypt, and a date near AD 60 is widely accepted. Erythraean was the Greek name for the Red Sea and, in this book, for the whole sea from the Red Sea to the Indian Ocean. The author names the best times to sail from Egypt to catch the monsoon winds, which shows first-hand knowledge.

The ports it describes run from the Indus delta to the east coast.

• Barbaricum: Present-day Karachi.
• Barygaza: Present-day Bharuch in Gujarat, one of the most active ports, importing wine, copper, tin, lead, coral and coin, and exporting spikenard, ivory, agate, cotton cloth and long pepper.
• Muziris: A Chera port on the Malabar coast, traditionally placed at Kodungallur and now often placed at Pattanam after excavations between 2007 and 2015.
• Arikamedu: Near Puducherry on the east coast, the port the Periplus calls Poduke.

On the Malabar coast, pepper and malabathrum drew large ships, and the Periplus lists the exchange in two directions.

Muziris, Pattanam and the Evidence from Excavations

Muziris appears in the Periplus, in Pliny and in Sangam poetry as Muciri. The Tamil poems describe the beautiful vessels of the Yavanas arriving with gold and leaving with pepper. A second-century papyrus even records a cargo loan between merchants of Alexandria and Muziris. Survey and trial excavations at Pattanam in 2003‑04 recovered parts of a Roman amphora, the first of its kind in Kerala, along with Chera period coins and pearls. Larger excavations by the Kerala Council for Historical Research between 2007 and 2015 recovered amphora fragments, fragments of Roman glass, carnelian intaglios, square copper Chera coins and botanical remains of black pepper.

The site of Muziris is disputed. Some scholars place it at Kodungallur, where later Jewish copper plates name a port called Muyirikkode, and the Pattanam finds are dated from the third century BC to the fifth century AD. Pattanam is therefore believed, not proven, to be Muziris.

South India was never part of the Roman Empire, yet there were close connections through trade, and hoards of Roman coins found at archaeological sites in south India bear witness to them.

The Decline of Indo-Roman Trade

The Indo-Roman trade declined from the mid-third century, during a crisis in the Roman Empire. It recovered in the fourth century and continued until the early seventh century, when the Sasanian king Khosrow II occupied the Roman parts of the Fertile Crescent and Egypt, through which the trade passed. The Eastern Roman emperor Heraclius defeated him at the end of 627 and recovered those lands, but the Arab conquest of Egypt, begun in late 639 or early 640, ended about 670 years of Roman trade with the subcontinent.

As the old link weakened, Tamil-speaking south India turned to Southeast Asia for its international trade. There Indian culture left a far deeper mark than it had on Rome, seen in the adoption of Hinduism and then Buddhism. Knowledge of India was nevertheless preserved in Byzantine books.

After Rome: Transmission of Roman Geography

From Alexandria to Baghdad and Back

Ptolemy's Geography survived through three civilisations. In late antiquity the Alexandrian writer Pappus produced a commentary on it, and Cassiodorus, writing around AD 560, advised readers to consult the codex of Ptolemy, which described places so clearly that its author seemed a resident of all regions. Later imperial writers merely commented on the text, and surviving records show decreasing fidelity to real positions.

In the ninth century the Geography and the Almagest were translated into Arabic. At the court of the caliph al‑Ma'mun in Baghdad, al‑Khwarizmi, who worked at the House of Wisdom around 820, compiled a Book of the Depiction of the Earth that imitated Ptolemy by giving coordinates for 545 cities. A coloured world map made under al‑Ma'mun, described by al‑Mas'udi, was said to be superior to the maps of Marinus and Ptolemy and included 4,530 cities and over 200 mountains.

In the twelfth century the Almagest returned to Europe in Latin from the Arabic, finished by Gerard of Cremona at Toledo in 1175, and the Geography was translated from Arabic into Latin at the court of Roger II of Sicily, though no copy of that translation survives.

Renaissance Europe, Print and the Columbus Connection

Ptolemy's Geography reached Latin Europe by a second route. The Byzantine monk Maximus Planudes searched for a copy in the summer of 1295 and redrew the maps from the coordinates in the text. The Greek text reached Florence about 1400, and the first Latin translation was made in 1406 or 1407 by Jacobus Angelus.

Print then spread the Geography across Europe.

• Bologna, 1477: The first printed edition with maps, and also the first printed book with engraved illustrations.
• Ulm, 1482: The first edition printed north of the Alps, and a commercial success.
• Strasbourg, 1513: An edition that added 20 modern maps beside the old ones.

Other Roman works returned too. Mela's De situ orbis was first printed at Milan in 1471, a Latin translation of Strabo commissioned by Pope Nicholas V appeared around 1469, and its first Greek printing followed in 1516.

Ptolemy's authority carried his errors forward. His approval of the smaller circumference, rather than the earlier and more correct figure of Eratosthenes, made it the accepted value for the next 1,500 years. Columbus used the same smaller figure and so put the distance to India at only 70,000 stadia.

Columbus also adopted Marinus's longitude of 225 degrees for the east coast of the Great Gulf and used a shorter length for the degree. By this reasoning he placed eastern Asia and Japan about 90 and 60 degrees west of the Canary Islands, far nearer than they are. An old dispute over the size of the Earth therefore helped to launch the voyages of the age of exploration.

Contributions of Roman Geographers to Geography

Comparison of Strabo, Mela, Pliny and Ptolemy

The four geographers whose works survive differ most in method. Strabo and Mela described lands from travel and from earlier writers, Pliny compiled what others had written, and Ptolemy fixed places by coordinates. Each method produced a different kind of geography and a different kind of error.

Marinus of Tyre is not among them because his work is lost; it is known only through Ptolemy's Geography, which drew on it.

Five Contributions and Their Limits

The contributions of the Roman geographers can be grouped under five heads, and together they turned scattered Greek ideas into a body of knowledge that the Arabs and the Renaissance could inherit.

• Regional geography: Strabo's description of each land as a whole, with its people, places and resources.
• Encyclopaedic compilation: Pliny's gathering of earlier knowledge with named sources and an index.
• Mathematical geography: Marinus and Ptolemy's latitude, longitude, gazetteer and projections, the base of later cartography.
• Practical survey: Roads, the groma, centuriation and itineraries, geography put to work for administration.
• Knowledge of Asia: Records of India, Sri Lanka and the trade routes preserved in the Periplus, Pliny and Ptolemy's Book 7.

The limits belong with the contributions. The Earth was too small in Ptolemy's map, the Indian Ocean was closed, and the Roman geographers rarely reconciled description with measurement. Even so, the frame they built lasted until the voyages of the fifteenth and sixteenth centuries.

Roman Geographers in Geography Optional and General Studies

For Geography Optional Paper I the Roman geographers belong to the evolution of geographical thought, between the Greek founders and the Arab geographers. The usual question asks for their contributions or for a comparison of Strabo and Ptolemy.

For General Studies, the topic connects to three other areas. Ancient history uses Pliny, the Periplus and Muziris for Indo-Roman trade. Physical geography uses Eratosthenes's circumference and the idea of a spherical Earth. And the study of maps uses Ptolemy's grid, with its equator for latitude and its prime meridian through the Fortunate Isles.

Sources

• NCERT: Fundamentals of Physical Geography (Class XI), Geography as a Discipline
• NCERT: Themes in Indian History I (Class XII), Kings, Farmers and Towns
• Wikipedia: Al-Khwarizmi
• Wikipedia: Almagest
• Wikipedia: Arikamedu
• Wikipedia: Antonine Itinerary
• Wikipedia: Centuriation
• Wikipedia: Cursus publicus
• Wikipedia: Eratosthenes
• Wikipedia: Geographica
• Wikipedia: Geography (Ptolemy)
• Wikipedia: Groma (surveying)
• Wikipedia: Hippalus
• Wikipedia: Hipparchus
• Wikipedia: History of geography
• Wikipedia: Indo-Roman trade relations
• Wikipedia: Marcus Vipsanius Agrippa
• Wikipedia: Marinus of Tyre
• Wikipedia: Muziris
• Wikipedia: Natural History (Pliny)
• Wikipedia: Pattanam
• Wikipedia: Periplus of the Erythraean Sea
• Wikipedia: Pliny the Elder
• Wikipedia: Pomponius Mela
• Wikipedia: Posidonius
• Wikipedia: Ptolemy
• Wikipedia: Ptolemy's world map
• Wikipedia: Pythagoras
• Wikipedia: Roman roads
• Wikipedia: Strabo
• Wikipedia: Tabula Peutingeriana
• Wikipedia: Taprobane
• NOAA National Ocean Service: History of geodesy
• U.S. Geological Survey: Map projections
• UNESCO Memory of the World: Tabula Peutingeriana
• Department of Archaeology, Government of Kerala: Explorations and excavations
• UPSC: Civil Services Examination question papers