The earliest known boats were propelled by oars. Sails were soon discovered, probably in Egypt, where a light, but steady, north wind blows up the Nile. The Egyptians found that by stretching a large mat across the ship they could proceed up the river. However, sails remained an auxiliary source of power until about 300 A.D. because they could be used only with a following wind. Fig. 1 shows an Egyptian ship of about 1600 B.C.

The next improvement came in China, where the square sail was turned fore and aft, enabling the boat to be sailed at an angle to the wind. Unfortunately the Chinese made no further improvements, and the junk, Fig. 2, has remained basically unchanged for about two thousand years.