In the middle of the 4th century, Saxons settled in here, wreaking havoc among the inhabitants. So, Romans decided to raise a fortress called Grannona, where people took shelter in case of war.
Guérande was implicated in Brittany's War of Succession: in 1371, duke Jean III passed away, childless. A merciless battle began for the throne, between Charles de Blois, supporting king of France Philip VI, and Jean de Montfort who supported king of England Edward III. In the little church, the treaty of Guérande was signed, in 1365: the end of the war... Then, Jean de Montfort was crowned duke of Brittany.
Well, nowadays we still can see the granite walls (1 300 metres long), raised by Jean V de Montfort in 1431. 10 towers left, plus 4 gates: porte vannetaise, to the North; porte Saint-Michel, to the East (built by duke François II, which used to be the governor's house); porte Bizienne and porte de Saillé.