According to Claudius Ptolemy, Diogenes, a merchant in the Indian trade, was blown off course from his usual route from India, and after travelling 25 days south along the coast of Africa arrived at Rhapta, located where the river of the same name enters the Indian Ocean opposite the island of Menouthias. Diogenes further describes this river as having its source near the Mountains of the Moon, near the swamp whence the Nile was said to also have its source.