Hippalus was a Greek navigator who probably lived in the 1st century BCE. He is sometimes conjectured to have been the captain of the Greek explorer Eudoxus of Cyzicus' ship.

The writer of the Periplus of the Erythraean Sea credited Hippalus with discovering the direct route from the Red Sea to India over the Indian Ocean. by plotting the scheme of the sea and the correct location of the trade ports along the Indian coast. Pliny the Elder claimed that Hippalus discovered not the route but the Monsoon wind also called Hippalus. Most historians have tried to reconcile the reports by stating that knowledge of the monsoon winds was necessary to use the direct route, but the historian André Tchernia explains that Plinius' connection between the wind and the navigator was based on common pronunciation: in the Hellenistic Era the name of the wind was written as Hypalus, only in Roman times the spelling Hippalus came in use. The wind had already been known in Hellenistic times and had before been used by Arab and Indian sailors to cross the Indian Ocean. 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. Hippalus was probably the first (in the west) to recognize the north-south direction of India's westcoast. Only someone who has this insight will think crossing the Indian Ocean might be a faster way to (southern) India than following the coastline.

The use of Hippalus' direct route greatly contributed to the prosperity of trade contacts between Greco-Roman Egypt and India from the 1st century BCE onwards. From Red Sea ports like Berenice large ships crossed the Indian Ocean to the Tamil kingdoms of the Pandyas, Cholas and Cheras in present day Kerala and Tamil Nadu.

In modern times a crater on the moon was named after the navigator.

Reference

• Federico De Romanis and André Tchernia, Crossings: Early Mediterranean Contacts with India (New Delhi 1997)