The Siege of Bourg, 1406
J.L. Kirby describes an episode in the long struggle of the English Kings to keep their fiefs as Dukes of Aquitaine.
In May 1152 Henry, soon to be King of England, married Eleanor, heiress to the Duchy of Aquitaine. Henceforth for almost exactly three hundred years the Kings of England were also Dukes of Aquitaine, and as such vassals of the Kings of France. But as the French monarchy grew in power, the Kings came more and more to resent the existence of a vassal who was also a King in his own right.
In the fourteenth century, if not in the fifteenth, the English presence in this duchy (now usually called Guyenne, or simply Gascony) was one of the main causes of war between the two countries; and the French made persistent attacks on its borders.
So that in spite of the successes of Edward III and of his eldest son, the Black Prince, who served as lieutenant of Aquitaine, the duchy was getting slowly and steadily smaller. Moreover, as there was no settled frontier, it is almost impossible to determine what the boundaries were at any given moment.