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
Flooding of the Nile August causing enormous precipitations on the Ethiopian Highlands whose summits reach heights of up to 4550 m (14,928 ft). Most of this rainwater is taken by the Blue Nile and by the Atbarah River into the Nile, while a less important amount flows through the Sobat and the White Nile into the Nile. During this short period, those rivers contribute up to ninety percent of the water of the Nile and most of the sedimentation carried by it, but after the rainy season, dwindle to minor rivers. These facts were unknown to the ancient Egyptians who could only observe the