A road leads west through the Maidan from the top of Park Street to the gates of Fort William . As the fort functions as the military headquarters of the Eastern Command, entry is restricted and the public is only allowed into certain sections on special occasions. Built on the site of the old village of Govindapur, and commissioned by the British after their defeat in 1756, the fort was completed in 1781 and named after King William III. A rough octagon, about 500m in diameter, whose massive but low bunker-like battlements are punctuated by six main gates, the fort was designed to hold all the city's Europeans in the event of attack. To one side it commanded a view of the Maidan, cleared to give a field of fire; to the other it dominated the river and its crucial shipping lanes. Water from the river was diverted to fill its surrounding moat. Eighteenth- and nineteenth-century structures inside include the Church of St Peter's (now a library), barracks and stables, an arsenal, strong rooms and a prison. Today, the army still controls the Maidan and any special construction or activity must be approved by them.