The "Martello" towers that line the Irish coast at intervals north and south of Dublin (12 to the north, 16 to the south) were built in the early years of the 19th century by the British government, then under the leadership of "Billy Pitt" (Prime Minister William Pitt the Younger), to protect against the threat of invasion "when the French were on the sea."

JH 2011

An eighteen-pounder mounted atop the Martello tower on Killiney Hill, County Dublin, southwest of Dalkey, after restoration and inauguration in 2008. Source: daithaic.blogspot.com.

Gun firing from the same tower. Source: daithaic.blogspot.com.