East Friesland (frēzˈlənd) [key], Ger. Ostfriesland, region and former duchy, c.1,100 sq mi (2,850 sq km), Lower Saxony, NW Germany, on the North Sea. It includes the East Frisian Islands and is separated in the west from the Netherlands by the Dollart, an inlet of the North Sea formed by the Ems estuary. Emden, a port and shipbuilding center, is the region's chief city. The extensive moors and marshlands of East Friesland have been partly reclaimed. Cattle raising, sheep raising, and farming are carried on, and there are fisheries along the coastline. East Friesland became a county of the Holy Roman Empire in 1454, was raised to a duchy in 1654, passed to Prussia in 1744, and—after various transfers during the French Revolutionary Wars—was attached to Hanover in 1815.