Scapa Flow (Old Norse: Skalpaflói) is a body of water in the Orkney Islands, Scotland, United Kingdom, sheltered by the islands of Mainland, Graemsay, Burray, South Ronaldsay and Hoy. It is about 312 square kilometres (120 sq mi). It has a shallow sandy bottom not deeper than 60 metres (200 ft) and most of it about 30 metres (98 ft) deep, and is one of the great natural harbours/anchorages of the world, with sufficient space to hold a number of navies. Viking ships anchored in Scapa Flow more than 1000 years ago, but it is best known as the site of the United Kingdom's chief naval base during World War I and World War II. The base was closed in 1956.
The Viking expeditions to Orkney are recorded in detail in the 11th century Orkneyinga sagas and later texts such as the Hákonar saga Hákonarsonar. According to the latter, King Haakon IV of Norway anchored his fleet, including the flagship Kroussden that could carry nearly 300 men, at St Margaret's Hope on 5 August 1263 where he witnessed an eclipse of the sun prior to sailing south to the Battle of Largs. En route back to Norway Haakon anchored some of his fleet in Scapa Flow for the winter, but he died that December whilst staying at the Bishop's Palace in Kirkwall. In the 15th century towards the end of Norse rule in Orkney, the islands were run by the jarls from large manor farms some of which were sited at Burray, Burwick, Paplay, Hoy and Cairston (near Stromness) to guard the entrances to the Flow.