Historically, Guînes was the capital of a small county of the same name.
After the Romans left, in the 5th century, there is little known about the town. In the Dark Ages, according to legend, the territory of Guînes became the property of one Aigneric, Mayor of the Palace of the Burgundian king Théodebert II.
In 928, when the Danes invaded and seized the place, it was probably a defenceless village. A fenced mound and a double ditch would soon have been created by the Danes. This is the origin of the castle of Guînes. Arnulf I, Count of Flanders, realizing a counter-attack would be costly, arranged the marriage of his daughter Elstrude, to Sigfrid, the Danish leader, bestowing upon him the title of Count of Guînes but as vassal to him, the Count of Flanders. Under Sigfrid’s successors, the county of Guînes acquired considerable importance. At the beginning of the 11th century, Count Manassès founded a convent of the order of Saint-Benoit. This was placed under the jurisdiction of the nearby abbey of Saint Léonard. At that time, Guînes comprised three parishes within its walls, whose churches were dedicated to Saint Bertin, Saint Pierre and Saint Médard. Outside the town ramparts were the abbey of Saint Léonard, the church of Saint-Blaise, in the hamlet of Melleke, and the leper-house of Saint Quentin, in the hamlet of Spelleke (in Tournepuits).
At the end of 11th century, Baudoin II built a huge stone castle on top of Sigfrid’s old keep and enclosed the town within a stone wall, with defensive towers at each of the entrances. His son Fulk was a participant in the First Crusade.
In 1360, the Treaty of Brétigny surrendered the city and its county to England and they eventually became part of the Pale of Calais, the last English possession in mainland France. When the French captured the town of Calais in January 1558, Guisnes held out, by the courageous efforts of the English commander, William Grey, 13th Baron Grey de Wilton. After a few days of desperate fighting, however, Grey was wounded and his soldiers refused to fight on. The French gave honourable terms of surrender and English rule of the area came to an end.