Built with granite in the second decade of the 1800's, the Castle Breakwater and St Peter Port Lighthouse were created in response to a possible invasion of French forces under the direction of Napoleon.
The lighthouse - used as an aid to shipping, has a focal plane height of 14m above Mean High Water Springs (MHWS), and a range of 16NM (easily seen on clear evenings on rounding Corbiere Point in Jersey). It has a continuous light showing white for 7.5 seconds and red for 2.5 seconds, and a 12m (40 ft) round granite tower with lantern and gallery. During restricted visibility, a horn is sounded once every 15s to assist vessels in restricted visibility - activated manually by Guernsey Port Control.
The northeast face of the lighthouse is painted white, and vertical black and white stripes are painted on the head of the pier to make a more conspicuous day mark.
As well as being an important aid to shipping, the lighthouse is also a popular local fishing spot.