Strabo and Pliny believed that Africa terminated under the torrid zone, and that the Atlantic and Indian oceans joined. Ptolemy, as we have just seen, rejected this idea, and following the opinion of Hipparchus, that the earth was not surrounded by the ocean, but that the ocean was divided into large basins, separated from each other by intervening land, maintained, that while the eastern coast of Africa at Cape Prasum united with the coast of Asia at the bay of the Golden Chersonesus, the western coast of Africa, after forming a great gulf, which he named Hespericus, extended between the east and south till it joined India. The promontory of Prasum was undoubtedly the limit of Ptolemy's knowledge of the east coast of Africa: the limit of his knowledge of the west coast is not so easily fixed: some suppose that it did not reach beyond the river Nun; while others, with more reason, extend it to the Gulf of St. Cyprian, because the Fortunate Islands, which he assumed as his first meridian, will carry his knowledge beyond the Nun; and because, at the Gulf of St. Cyprian, the coast turns suddenly and abruptly to the east, in such a manner as may be supposed to have led Ptolemy to believe that it stretched towards and joined the coast of India. Of some of the interior parts of Africa Ptolemy possessed clear and accurate information; regarding others, he presents us with a mass of confused notions. He clearly points out the Niger, though he fixes its source in a wrong latitude. In the cities of Tucabath and Tagana, which he places on its banks, may perhaps be recognized Tombuctoo and Gana. The most striking defect in his geography of the interior of Africa is, that he does not allow sufficient extent to the great desert of Sahara, while the southern parts are too much expanded. He places the sources of the Nile, and the Mountains of the Moon in south latitude thirteen, instead of north latitude six or seven; but the error of latitude is not so remarkable and unaccountable as the very erroneous latitude which he assigns to Cape Aromata, on a coast which was visited every year by merchants he must have seen at Alexandria. The most difficult point to explain in Ptolemy's central Africa is the river Gir, which he describes as equal in length to the Niger, and running in the same direction, till it loses itself in the same lake. What this river is, geographers have not agreed. It is mentioned by Claudian, as resembling the Nile in the abundance of its waters. Agethimedorus, a geographer of the third century, regards it and the Niger as the same river.