Strabo, whose Geography is the main surviving source of the story, was skeptical about its truth. Modern scholarship tends to consider it relatively credible. During the 2nd century BC Greek and Indian ships met to trade at Arabian ports such as Aden (called Eudaemon by the Greeks). Attempts to sail beyond Aden were rare, discouraged, and involved a long and laborious coast-hugging journey. Navigators had long been aware of the monsoon winds. Indian ships used them to sail to Arabia, but no Greek ship had yet done so. For the Greeks to acquire the expertise of an Indian pilot meant the chance to bypass the Arabian ports and establish direct commercial links with India. Whether or not the story told by Poseidonius of a shipwrecked Indian pilot teaching Eudoxus about the monsoon winds is true, Greek ships were in fact soon using the monsoon winds to sail to India. By 50 BC there was a marked increase in the number of Greek and Roman ships sailing the Red Sea to the Indian Ocean.