As European traders and conquerors spread around and across other continents, they were brought into regular social contact with settled communities of people whose outward physical appearances greatly differed from their own. Black African slaves were known already in the Roman and Persian empires, and in medieval Christian and Muslim states. Europeans met Chinese traders in other lands long before regular direct contact was established with China. Chinese and Indians were in contact from at least the fifth century, both through sea-borne trade and through the journeys of Buddhist pilgrims. Some of the Indonesian islands were well known to the Chinese, and in the fifteenth century Chinese fleets visited the east coast of Africa. Communications across the Indian Ocean, between southern India and East Africa, were much older than this. The people of Madagascar were partly of Malaysian origin. It was not until the sixteenth century that considerable numbers of Europeans got to know sub-Saharan African and Far Eastern countries; and it was in the same period that other Europeans found and conquered the civilisations of the Americans. There grew up in the following centuries the idea that human beings were divided into ‘white’, ‘black’, ‘yellow’, ‘brown’ and ‘red’ races.