Portland Harbour is beside the Isle of Portland, Dorset, on the south coast of England. Construction of the harbour began in 1849; when completed in 1872, its 520-hectare (1,300-acre) surface area made it the largest human-made harbour in the world, and it remains one of the largest in the world today. It is naturally sheltered by Portland to the south, Chesil Beach to the west and mainland Dorset to the north. It consists of four breakwaters: two southern and two northern. These have a total length of 4.57 km (2.84 mi) and enclose approximately 1,000 ha of water.