The monsoon, and its accompanying winds, provided a regular and reliable way for boats to cross the Indian Ocean. At some point before 100 BC, mariners discovered that it was possible to sail directly to India, cutting across the Indian Ocean, rather than following the coast.

Taking their courage in their hands, sailors had sailed out into the Arabian Sea in late spring, leaving the sight of land behind. Through most of history, mariners were better described as coasters, hopping along beside the land and rarely leaving sight of it. Only three peoples in history discovered blue-water navigation: the Norse, the Polynesians and the Portuguese. The Indian Ocean mariners were not true blue-water navigators, but what they had discovered was the rhythm of the monsoon. In late spring and early summer, India heats up. Hot air rises off the panting earth and pulls in moist, cool air from the south-west. Mariners discovered that if they put out into the Arabian Sea at the right time of year, they could hitch a ride with the steady north-east winds blowing up to India. These late spring, early summer north-easterlies blow steady and true, carrying ancient sailors to the ports along the coast of north-western India and monsoon rain, blessed, holy rain to the parched interior.

Merchants riding the monsoon winds arrive in India in the summer, renew their old contacts, sell, buy and wait. They wait for the hot earth to cool down as summer draws down to autumn. Then, as the ground cools, in October and November, dry, cool air blows down from the Himalayas, out over the sea: regular, reliable winds blowing south-west to carry the ships and the merchants back over the ocean.

The monsoon cycle allowed merchants to make regular trips to and from India within six months, thus freeing the other half of the year to sell on the goods bought from the great trading ports in India to merchants selling into the Mediterranean and beyond.