c. AD 100–170
The eight books of Ptolemy’s Geographia provide our best account of the state of geographical knowledge in the 2nd century AD. But more than just repeating what was already known, Ptolemy strove to achieve the accurate measuring and recording of coastlines, cities, rivers and mountains. He set standards for practical geography, for the assessment of evidence, and for the management of information that later geographers strove to meet over the next 1500 years.
For centuries afterwards, the calculations, discoveries and groundbreaking scientific works produced by Ptolemy – Claudius Ptolemaeus of Alexandria – were forgotten knowledge in Western Europe. There are no original manuscripts, and the Geographia survived only in Arabic translations from much later. Out of Arabic, the work was subsequently translated into Greek, and then, in the early 15th century, from Greek into Latin.
Although Ptolemy left no maps of his own, his description of the three continents of Europe, Asia and Africa, and his calculations of the location of some 8000 different towns, rivers, mountains, and headlands were the intellectual foundation on which a great development of new cartography was constructed in the Renaissance. Respect for him was almost universal among Renaissance scholars, and afterwards. Before Gerard Mercator produced his own Atlas of the world in the late 16th century (see page 86), he spent more than seven years compiling a book of maps based entirely on the work of the man who became known as the ‘Father of Geography’. Even as the map-makers who charted the great discoveries of the 16th century were proving the inadequacy of Ptolemy’s vision of the world, they still looked up to him as the ancient fount of geographic wisdom.
Ptolemy was either Greek or Egyptian by descent, and he lived in the cosmopolitan Roman-Greek city of Alexandria, on Egypt’s Mediterranean coast, during the 2nd century. The precise dates of his birth and death are unknown, as are all the other facts about his life. But he was evidently a man of wide interests, for the books he left behind dealt with geography, astronomy, mathematics, astrology, physics and music – virtually the whole range of contemporary learning.
The Geographia, in particular, reveals a talented artisan and experimental thinker, as well as a dedicated scholar. Ptolemy was well aware that the geographical knowledge of his day extended at best over only about a quarter of the globe. The known world stretched from the ‘Fortunate Isles’ in the western Atlantic (probably the Cape Verde Islands) to central China in the east, and from the Shet-lands in the north to the eastern coast of Africa in the south. But much was based on conjecture or unreliable reports. Where reliable measurements could be obtained, he said, the map-maker should rely on them: elsewhere, he would have to use his judgement as to what figures to use, ‘deciding what is credible and what is incredible’.
At the beginning of the Geographia, Ptolemy sets out his intention to represent the known world as accurately as he can, and also to record the observations of ancient travellers. Accurate measurement, he says, rather than the philosophical pondering of his predecessors, is the true key to geography.
It is the prerogative of Geography to show the known habitable earth as a unit in itself, how it is situated and what is its nature; and it deals with those features likely to be mentioned in a general description of the earth, such as the larger towns and the great cities, the mountain ranges and the principal rivers. Besides these it treats only of features worthy of special note on account of their beauty … Now, as we propose to describe our habitable earth, and in order that the description may correspond as far as possible with the earth itself, we consider it fitting at the outset to put forth that which is the first essential, namely, a reference to the history of travel, and to the great store of knowledge obtained from the reports of those who have diligently explored certain regions; whatever concerns either the measurement of the earth geometrically or the observation of the phenomena of fixed localities; whatever relates to the measurement of the earth that can be tested by pure distance calculations to determine how far apart places are situated; and whatever relations to fixed positions can be tested by meteorological instruments for recording shadows.
GEOGRAPHIA, BOOK 1, I–II, TRANSLATED BY E.L. STEVENSON, 1932
Much of the material in the Geographia was directly derived from earlier scholars: Ptolemy saw his role as collecting and preserving scientific thought as well as developing his own theories. But, unlike his predecessors from the classical age, he believed that geography was essentially a mathematical enterprise, depending on accurate measurement and calculation. The location of a place, he knew, could be fixed by taking precise observations of the stars, and he constructed a grid to cover the world – an early form of latitude and longitude. Since his figures have been altered, improved, and miscopied by generations of scribes, it is impossible to know how accurate he was; but one short extract, dealing with the path of the Danube in Germany, demonstrates that it was a work of staggering ambition – the first time anyone had used mathematical coordinates in such a way:
The headwaters of the Danube 30° 0′ 46° 20′
Alongside where the river first turns into Germania 32° 0′ 47° 15′
Where the river turning bears towards the south, being called Ainos 34° 0′ 47° 20′
Where the river turning bears towards the north and another river against the Gambretan Forest, 36° 0′ 46° 40′
Next where the river turning against the Lunan Forest by a mountain stream from the north, 39° 20′ 47° 20′
For all Ptolemy’s ambitions, the Geographia is strewn with mistakes – most of them due to the unreliability of the information on which he had to rely. He underestimated the circumference of the world by some 25 per cent, and exaggerated the length of the Mediterranean and the distance across Asia – mistakes which, by drastically reducing the west-to-east distance across the Atlantic to the ‘Indies’, may have encouraged Christopher Columbus to set out on his great voyage of 1492.
It is not known whether there were any maps in the original book but the Geographia was planned, too, as a practical handbook of geography, in which Ptolemy gave precise instructions as to how they should be constructed. He knew that the world was round, not flat, and laid down guidelines for constructing a globe to show it in three dimensions – although he warned future geographers that they would find a globe either too small to fit enough information on, or too big to be of any use. Better by far, he said, to represent the round world on a flat sheet of paper – and the mathematically-designed projections that he designed for doing so remained the basis of most serious cartography until Mercator designed his own projection some 1450 years later.
Ptolemy’s view of the physical world dominated Western geography for almost 1500 years, and the Geographia still provides historians with most of what they know about how his contemporaries understood their world. Despite the shortcomings of his magnum opus, Ptolemy proposed a scientific method that represented a huge leap forward in gathering, assessing and combining knowledge. The real importance of the Geographia, however, was that it raised the possibility of a world outside. Geographers before Ptolemy had presented a view of a finite world, with the encircling waters of one great ocean, ‘Oceanus’, lapping at its shores. Ptolemy introduced the concept of terra incognita, the ‘unknown lands’ beyond the sea that explorers would one day reach.