Since the Norman Conquest of 1066, English monarchs had held titles and lands within France, the possession of which made them vassals of the kings of France. Over the centuries, English holdings in France had varied in size, but by 1337 only Gascony in south western France and Ponthieu in northern France were left. Following a series of disagreements between Philip VI of France and Edward III of England, on 24 May 1337 Philip's Great Council in Paris agreed that the Duchy of Aquitaine, effectively Gascony, should be taken back into Philip's hands on the grounds that Edward was in breach of his obligations as a vassal. This marked the start of the Hundred Years' War, which was to last one hundred and sixteen years.