Fort Frontenac is a small fort in (and the historical epicentre of) downtown Kingston which was occupied by the French from 1673 to 1758, the British from 1758(-ish) to 1871 and Canada since then. It also played a role in US history as the base for LaSalle's explorations. It is a working military base still and must be one of the military's longest continuously occupied spots in the country - perhaps in North America. The ruins of one of the French palisades has been preserved across Ontario Street from the current front gate.
1673-1758 French Fort ruin at Ontario Street and Place D'Arme
Fort Frontenac from the water...
...and from Ontario Street
Below are three things on the walls. Left is some marking on a corner post which I do not understand. Centre is a well buffed brass plaque to a stay by the New York Rangers (the military ones) in 1760. Right is a not so gleaming copper one to the formation of the first Canadian military unit in 1871 which was stationed here. Click on these three for a larger version. These sniper holes in the walls guard the Wolfe Island Ferry building next door.

Comments
Alan - April 30, 2004 8:36 AM
Here is an interesting bit of evidence from a New York heritgage bloggers. Governor's Island was the longest serving US base from 1794 to 1997. Fort Frontenac has definitely been occupied from 1783 to the present and also from 1673 to 1758 with periodic encampments between the two. So it may well be the longest servicing military post in North America.