Hippalus

To understand the importance of Hippalus' discovery we have to know that before him Greek geographers thought that the Indian coast stretched from west to east.

Only someone who has this insight will think crossing the Arabian Sea might be a faster way to south India than following the coastline.

The use of Hippalus' direct route greatly contributed to the prosperity of trade contacts between the Roman province of Aegyptus and India from the 1st century BCE onwards.

From Red Sea ports like Berenice large ships crossed the Arabian Sea to the Malabar coast and Muziris port, Tamil kingdoms of the Pandyas, Cholas and Cheras in present-day Kerala and Tamil Nadu.

[1] Hippalus is also a prominent character in L. Sprague de Camp's 1969 novel about Eudoxus, The Golden Wind.