The maps of the Greek writer and Roman citizen Ptolemy have not survived in their original form; those we have are medieval reconstructions. An accomplished astronomer and mathematician, he understood that the world of which he was aware was a fraction of the total. There are also substantial inaccuracies in his calculations of latitude and longitude. Understandably, the map becomes increasingly conjectural beyond the bounds of the classical Roman world: the Indian Ocean is depicted as a land enclosed sea, akin to the Mediterranean. Nevertheless, the mountain ranges of Central Asia are detailed with surprising accuracy, more so than the vague prognostication of ‘Scandia’. Whereas the size of Sri Lanka (‘Taprobane’) is vastly overestimated, its topography is approximately correct. The Malay Archipelago is depicted, and cities like ‘Sabana’ and ‘Cattigara’ probably reveal awareness of ancient thalassocracies in Selangor and Funan. The western boundary of Ptolemy’s world falls just beyond the ‘Fortunata’ islands, perhaps the Canaries; the Atlantic is not represented.