At Rue de la Tour, you'll find the only surviving vestige of the 12th century Grimaldi Castle.
The castle, owned by the County of Savoy, was given in fief to the Grimaldis in 1390. The remains of the surrounding walls and tower, remnants of the castle's military heritage, can still be seen from this street. They protected the Castrum (typical of 12th century Provence, since destroyed).