Historic capital and harbour town in the south of the Isle of Man, built around Castle Rushen.

Castletown developed at the head of Castletown Bay where the Silverburn enters the sea. Castle Rushen dominated the harbour and provided the seat of government, court, prison and residence of the Governor. The settlement which grew around it became the principal administrative town of the Island.

A church dedicated to St Mary was established at Rushen or Castletown by the thirteenth century. The church was dedicated in 1260 during the episcopate of Bishop Richard. Later descriptions record the old church, chapel and free school among the public buildings of the town.

The castle brought a concentration of officials into Castletown. The Governor, Deemsters, Attorney-General, Clerk of the Rolls and other officers attended courts there, while the House of Keys met close to the castle. Government business therefore took place within a few streets of the harbour.

Castletown bridge was described in the eighteenth century as a stone bridge of handsome breadth, sufficiently high for a boat carrying its mast to pass beneath it. Across the river stood the property later known as Bridge House, associated with the Quayle family and the yacht Peggy.

The harbour connected the town with the southern roadsteads at Derbyhaven and Ronaldsway. Castletown itself was one of the appointed ports of the Island, while nearby Derbyhaven provided a broader natural anchorage. The surrounding district contained many of the Island's principal southern estates and lay close to Rushen Abbey and the fertile plain around Malew.

Markets were held on Saturdays. One eighteenth-century account remarked that butcher's meat was commonly bought by several households joining together to purchase a whole carcass, while herrings and potatoes formed a much more regular part of the diet.

Castletown remained the seat of the Island's government into the nineteenth century, although Douglas increasingly overtook it in population and commerce.