Saint-Malo was named after a Welsh monk Mac Low, who, around the 6th century, established his bishopric in Alet, a stone's throw away from the rock where the walled city now stands. As early as the 13th century, the "Malouins" were already quite successful at catching enemy ships and in 1308 they instated a sworn allegiance to Charles VI King of France, who granted it a free commune to encourage the commercial activities of craftsmen as well as merchants and ship owners.
In order to keep the inhabitants under control, the Duchy of Brittany had the main castle built, which the Malouins then took over in 1590. They later declared themselves an independent republic, which lasted fours years until King Henri IV of France agreed to become a Catholic. Jacques Cartier, on his travels from 1534 to 1542, opened the Newfoundland route and discovered Canada.
Formerly called "Saint-Malo de l'Isle", the city, clustered around the cathedral only 16 hectares wide, burnt down for the first time in 1661. In the following years, architects Vauban and Garangeau re-constructed it and extended it to 24 hectares, in 4 stages.