The Porte de la Grosse Horloge, instantly recognisable due to its size, is a Gothic tower that once separated the port from the city.

It was initially designed to defend the town if it was attacked from the port, serving as the last rampart against an invasion. It outlived its usefulness, in particular after defences were built on the port itself. The three towers of La Rochelle were deemed quite capable of defending the city from invaders on their own.