Montréal, in the south-west corner of Québec Province, is situated on the largest of the 234 islands that form the Hochelaga archipelago in the St Lawrence River. The heart of the city is the Île de Montréal (158 sq. km (61 sq. mi.) at the confluence of the Ottawa River and the St Lawrence, which also takes in the slopes of the ancient volcano of Mont-Royal, or Mount Royal (238 m (260 ft)), the mountain park in the city centre.