After the complete destruction of the village Eidum by a storm surge on 1 November 1436, the survivors founded a new village northeast of their old home: Westerland.
South of Westerland, the island extends for about 15 km in the form of a spit, until it is cut by the Hörnumtief tidal creek, that runs through the Wadden Sea mudflats east of Sylt.