Traditional fishing boat were used for war and trade. Some ancient vessels were propelled by either oars or sail, depending on the speed and direction of the wind (see trireme and bireme). The Chinese were using sails around 3000 BC, of a type that can still be seen on traditional fishing boats sailing off the coast of Vietnam in Ha Long Bay. A jangada is an elegant planked fishing boat used in northern Brazil. It has been claimed the jangada dates back to ancient Greek time. It uses a triangular (lateen) sail, which allows it to sail against the wind. A felucca is
Cataracts of the Nile river bed exposed. These distinctive features of the river between Aswan and Khartoum have led to the stretch being often referred to as the Cataract Nile, while the downstream portion is occasionally referred to as the "Egyptian" Nile. The geological distinction between these two portions of the river is considerable. North of Aswan, the river bed is not rocky, but is instead composed of sediment, and far from being a shallow river, it is believed that the bedrock was previously eroded to be several thousand feet deep. This created a vast canyon that is now filled by the sediment, some