Tour Carbonnière, Medieval tower in Saint-Laurent-d'Aigouze, France.

The Tour Carbonnière is a 16-metre-high square watchtower built of light beige ashlar with projecting central bosses, standing in the marshes between the Vistre and the Rhône à Sète canal. The old road passed through a round-headed archway at its base, closed by a portcullis; above it a small square window lights the vaulted guardroom. Stone brackets support a slightly wider upper section with a parapet and a small dome.

The tower was built at the end of the 13th century as part of the fortifications of Aigues-Mortes. It served to protect the walled city and control passage through a toll system.

The tower's name may come from the "pont de la Carbonnière", a wooden bridge mentioned in a 1270 act, or from a 15th-century toll official under Charles VII. The monks of Psalmody kept the tower and collected a toll; from 1409 no traveller was exempt. Builders' marks on its stones match those on the Aigues-Mortes ramparts.

You can reach the tower by walking along a boardwalk path and climb to the viewing platform, which contains corner watchtowers and observation points. The climb is doable, though access depends on weather conditions and maintenance status.

The tower's ashlars carry mason's marks identical to those on the ramparts of Aigues-Mortes, since both were built from the same quarry at the end of the 13th century. Look for the carved rectangular recesses on the blocks of the façade.