Porte Saint-Denis, Mortagne-au-Perche, Fortified gate in Mortagne-au-Perche, France

The Porte Saint-Denis is a fortified gate on Rue du Portail-Saint-Denis in the centre of Mortagne-au-Perche, the last remaining vestige of the Fort Toussaint. Its 15th-century archway was given a two-storey Renaissance logis in the 16th century. The gate is built of rough grey stone pierced by a large pointed arch with voussoirs, above which smooth light stone carries four rectangular windows over four arched ones, with carved panels between; a steep brown tiled roof is flanked by two chimneys.

Built between the 12th and 13th centuries, it served as one of the principal entrances to Fort Toussaint and remains the only surviving structure from that fortification. The gate is an architectural trace of what was once a major defensive stronghold.

The building housed the Musée percheron, which was already installed when the town council took over its lease in 1937; the museum has been closed since the early 2010s. The two first-floor rooms with their Louis XVI-style wood panelling are covered by the 1975 listing, alongside the facades and roofs. The gate stands on Rue du Portail-Saint-Denis, and a sign reading "Mairie Percheoise" is fixed beside its wooden door.

The gate is easily reached on foot from Rue de la Porte-Saint-Denis in the town center. The surrounding area offers clear sightlines and space to view both the front and side facades from different angles.

The south-facing side originally had two corner towers that no longer exist today. Over time, the galleries on the north side were filled in with walls, significantly altering the gate's original appearance.