 Since the end of the 19th century, the Russian Empire began to build coastal fortresses and naval strongholds in Estonia which was annexed to the empire after the Great Northern War in 1721.Tallinn, having been historically an important trading center between the East and the West, became one of the main naval bases of the Imperial Russian Baltic fleet.A systematic coastal defence network and naval gun installations were ordered, and the construction works began at the end of the 1890s.