The Muiden West battery is a tower fort built around 1850 as a bomb-proof gun turret. The oval tower with its moat and drawbridge is across from Amsterdam Castle Muiderslot, on the other side of the river Vecht. The tower’s purpose was to defend the harbour entrance and the sea locks. One of the Defence Line of Amsterdam’s most remarkable elements, Fort Pampus (on the island opposite) was added in the late 19th century for additional protection and to close off the harbour entrance.