Built in the early-14th century by John Cockerham, the Abbot of neighbouring Furness Abbey, it was intended to oversee the trade through the local harbour and to protect against Scottish raids.

In the 1870s the castle's owner, the Duke of Buccleuch, carried out extensive restoration work and erected outworks to protect it against further damage from the sea.

[4] Comprising a keep with an inner and outer bailey, the castle was intended to oversee the trade through the harbour, and to provide defence, as the Abbey had faced raids from Scotland in 1316 and 1322.

[5] Architectural historian Anthony Emery argues that the castle was built in three phases, starting with the central keep, which he believes was intended as a largely unfortified summer residence for the Abbot.

[7] In 1408, the Abbot John Bolton decided that the cost of maintaining the castle was excessive, and attempted to pull down the defences, but was prevented from doing so by Henry IV; this was followed by a period of rebuilding around 1429.

[8] The castle was used for smuggling by the Abbey, leading to complaints from merchants in English-controlled Calais that they were illegally trafficking wool, which in this period could only legally be sold through the French port.

[10] He sought help from potential local supporters and held court at the castle, before advancing inland and ultimately being defeated at the Battle of Stoke Field.

[3] Walter Scott, the Duke of Buccleuch, purchased the rest of the island and carried out an extensive and expensive restoration of the castle between 1877 and 1878, destroying most traces of the medieval occupation of the site in the process.

[21] The castle is built to an Edwardian concentric design, with a keep in the south-eastern corner, protected by an inner and outer bailey with stone curtain walls extending out to the north-west.

[22] The castle is built using stones from the local beach bonded with a liquid mortar, with the finer stonework, such as the doorways and windows, made from red ashlar sandstone imported from the mainland.