La Rochelle lies on the Atlantic coast and has a fort dating from the Middle Ages. The harbour facilities were built in the 14th/15th century and defended from the two towers Tour St. Nicolas and Tour de Chaicircne. The chain between the towers prevented entry to the harbour at night, which even today accounts for much of the town's beauty. Sights include: the Porte de la Grosse-Horloge, the Tour de la Lanterne, the town hall, the St. Louis Cathedral, St. Sauveur church.