Knockalla Fort is one of several Napoleonic batteries built along the shores of Lough Swilly in county Donegal, to defend the north west of Ireland.

[1] It is triangular in shape with a tower on the landward salient angle.

From the tower, the two walls of the fort, protected by a dry moat partly cut into the rock, lead down to the edge of steep rocky cliffs, where there are batteries on two levels.

The upper level contains barrack accommodation, magazine, casemates, entrance gateway and an upper battery for two 24 Pounder smooth bore guns on the northern flank of this level.

The tower is quadrant-shaped in plan with corners rounded off and was armed with a 24 Pounder gun and a 5.5-inch howitzer.