 It stands at Coalhouse Point on the north bank of the river, at a location near East Tilbury which was vulnerable to raiders and invaders.It was the last in a series of fortifications dating back to the 15th century and was the direct successor to a smaller mid-19th century fort built on the same site.Constructed during a period of tension with France, its location on marshy ground caused problems from the start and led to a lengthy construction process.