The historic town of Forcalquier was built on the edge of the Via Domitia according to a semi-concentric plan on the slope of a hill. It surrounds the citadel that forms a set of fortifications surmounted by the octagonal chapel of Notre-Dame-de-Provence. The oldest part of the city extends under the citadel and consists of narrow streets and squares bordered by houses that sometimes date back to the 14th century. The 12th-century Notre-Dame du Bourguet co-cathedral dominates the old town with its square bell tower.