Summer Siege is the Canton of Harrowgate Heath's yearly melee event. Also found is thrown-weapons tournaments, archery tournaments, and an equestrian demo.

Summer Siege focuses on melee fighting, though the scenarios change annually. Past themes have included a castle siege battle and boat wars. Starting in AS XLVI a 'peasant battle' was added where the attending populace could throw 'rocks' at the fighters as they fought; this proved quite popular and will most likely be a recurring battle.

Originally held at Michael Eastbrooke's farm, Summer Siege then spent a couple of years at the Chesterville Fair Grounds. Starting in 2013, it is now held at John Wood's farm in Kemptville, ON.

Usually held on the second or third weekend of June.