One well-preserved 500m/1,640ft-section of the Roman wall can be seen here by the River Sarthe. Its ochre sandstone held together by pink mortar earned it the name of "red city", like Bourges, Limoges and Lyon. This section was part of the wall built between 270 and 310 that encircled the city for 1,300m/4,265ft, measuring 4m/13ft at its base and dotted with 26 towers. At the end of the tunnel, Yssoir Bridge offers a view of the wall and cathedral.