Tour Saint-Nicolas, Medieval defense tower in La Rochelle, France.

The Tour Saint-Nicolas is a tall cylindrical stone tower of pale gray weathered masonry rising from a lower base at the mouth of the Old Port. Its top carries a projecting parapet with corbels and crenellations, and two smaller crenellated turrets flank the main shaft, one on the right and one at the left rear. Narrow vertical slit windows are cut in rows into the stone, and a single small projecting stone spur marks the front face. A low stone wall connects to the base on the right.

Construction began around 1345 on oak piles driven into marshy ground; the foundations gave way and the tower still leans east by more than 20 cm. The 1360 Treaty of Brétigny ceded La Rochelle to England and halted work until 1372, when Charles V's alliance with the town resumed it. The tower was finished in 1376 and housed its first captain and garrison in 1384.

The Tour Saint-Nicolas remains one of three medieval towers in La Rochelle that represent the maritime defense architecture of the French Atlantic coast.

Access to the upper levels requires climbing a steep interior staircase, so wear comfortable shoes and prepare for physical effort. The viewing platforms above offer good sight lines but can feel less comfortable during windy or stormy weather.

The tower leans more than 20 cm to the east because its oak-pile foundations gave way in the marshy ground; engineers stabilized the base and corrected the upper shaft's verticality instead of righting it. Legend credits the fairy Mélusine with building it. It later served as a prison.