Porte de Montreuil is a station on line 9 of the Paris Métro. The station has four lines, two of which are sidings, and is quite impressive in scale. Until recently it was an artificial rough-hewn cavern, but it has now been covered with plain white tiles. The station was opened on 10 December 1933 with the extension of the line from Richelieu - Drouot. It was the eastern terminus of the line until the extension of the line to Mairie de Montreuil on 14 October 1937. It is named after the Porte de Montreuil, a gate in the nineteenth century Thiers wall of Paris, which led to the town of Montreuil. Flea markets are held on the glacis (the sloping bank in front of a wall) of the fortifications.