EIDER, a river of north Germany in Schleswig-Holstein. It rises to the south of Kiel, in Lake Redder, flows first northward, nearly as far as Kiel, then bends westward and flows across the low peninsula in a sluggish, winding course of about 117 m. Tonning stands at the head of its long shallow estuary. It is navigable up to Rendsburg, and is embanked through the marshes across which it runs in its lower course. Since the reign of Charlemagne, the Eider (originally Agyr Dor—Neptune's gate) was known as Romani terminus imperil and was recognized as the boundary of the Empire in 1027 by the emperor Conrad II., the founder of the Salian dynasty. In the controversy arising out of the Schles wig-Holstein question, which culminated in the war of Austria and Prussia against Denmark in 1864, the Eider gave its name to the "Eider Danes," the intransigeant Danish party which main tained that Schleswig (Sonderjylland, South Jutland) was by nature and historical tradition an integral part of Denmark. The Eider canal (Eider-Kanal), which was constructed between and 1784, Ieaves the Eider at the point where the river turns to the west and enters the Bay of Kiel at Holtenau. It was ham pered by six sluices, but was used annually by some 4.000 vessels. and until its conversion in 1887-95 into the Kaiser Wilhelm canal afforded the only direct connection between the North sea and the Baltic. (See KIEL CANAL.)