The arch of the Porte Sainte Marie spans the Grand Rue, following the traces of the Roman's main road from Lausanne to Geneva, through Nyon. Many Roman-carved blocks are visible in the wall to the left of the road.

Originally, towers stood on either side of the arch, which was really a door frame, with a heavy wooden door to the town. In the 18th century, the house on the right (the Lake side) of the door was built: that tower was demolished, and the door removed.