Kingston Fortifications
The site of the Royal Naval Dockyard during the War of 1812, Kingston assumed even greater strategic importance as the southern terminus of the Rideau Canal, which was built between 1826 and 1832. An extensive fortification plan of redoubts, towers, and batteries was developed to protect the dockyard and entrance to the canal, but only Fort Henry was actually built. In response to the Oregon Crisis with the United States in 1845-1846, four Martello towers and the Market Battery, which stood on this site, were constructed between 1846 and 1848.
Plaque via Alan L. Brown's site Ontario Plaques. Full page here.