"The circular fort on St. Michael's Isle was first constructed in 1540's and rebuilt a centurry later.'
Source: 'Profile of Castletown' by Derek Winterbottom (ISBN:978-1-899602-39-1)
In the 1540's The Earl's of Derby were 'Lords of Man' having earlier in the century dropped the provocative title of 'King of Man' in order to stay on friendly terms with the English King Henry VIII.
It was The Earl Edward who was entrusted with the defence of north-west England in the 1540's and is 'credited with a good knowledge of artillery warfare' and was probably responsible for the strengthening of defences at the nearby Castle Rushen in Castletown and with ordering the construction of the circular fort.
Source: 'Profile of Castletown' by Derek Winterbottom (ISBN:978-1-899602-39-1)
The Fort was intended originally 'to repel potential attacks from France and Spain and formed a link in an extensive chain of coastal forts, though rather more still exist in southern England. The fort probably consisted of a gun emplacement housing a number of cannon to defend Derbyhaven Bay. In the 1640's, during the [English] Civil War, James Stanley 7th Earl of Derby and Lord of Man, embarked on the modernisation of many of the Island's defences, in an attempt to secure it for the Royalist cause against the Parliamentary forces. It is likely that he was responsible for re-arming the Fort with more powerful cannon, and for providing the loopholed walkway around the top of the fort for musketeers."
Despite the fact the walls of the Fort are three metres thick it is likely that the fort was nearing the end of life by 1660's given advances in military technology. At some time later the Fort was used as lighthouse when a small tower housing a light was constructed although sadly this tower has subsequently been demolished.
Source: 'A Guide to the Archaeological Sites of the Isle of Man up to AD 1550'by Andrew Johnson and Allison Fox (ISBN:978-0-9554043-5-1)
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