Carleton Martello Tower, Martello tower in Saint John, Canada.

Carleton Martello Tower is a circular masonry tower 30 feet high and 50 feet in diameter, begun in 1813 on a rocky cliff above Saint John to guard the land approaches to the city. It was completed in 1815, after the War of 1812 had ended, and the planned three 4-pounder and two 24-pounder guns were never installed. A bombproof magazine was built inside in 1846, and a two-storey concrete structure was placed on top in 1941.

Construction began in 1813 on a rocky cliff to guard Saint John's land approaches against an overland invasion from the United States, but the tower was not completed until 1815, after the War of 1812 had ended. It was the third link in the city's defences, with Fort Howe and Fort Dufferin. In August 1941 a two-storey concrete structure was added on top to serve as a Fire Command Post until August 1944.

The tower's name comes from Carleton, the Saint John district where it stands, and from the Martello design borrowed from a Corsican tower at Mortella. Its 50-foot-diameter circular masonry shell, 30 feet high, was meant for three 4-pounder and two 24-pounder guns that were never installed. A bombproof magazine added in 1846 served as the powder store from 1859 to 1866.

The tower sits atop a hillside and requires climbing a steep interior and exterior staircase to reach the top, which demands moderate fitness. A visitor center with exhibits and presentations provides context about the military history and helps visitors understand the site.

In August 1941 a two-storey concrete structure was placed on top of the tower so it could serve as a Fire Command Post, a role it held until August 1944. The tower received a No. 3 Mark 4 telescope and a No. 10 Director on 20 April 1942, and a Mark II Position Finder was added on 1 May 1943. Soldiers of the 3rd New Brunswick Coast Brigade manned it from 1941 until operations ceased in 1944.