The Treaty of Le Goulet was between King John I of England, and King Philip II of France, and took place on Gueuleton Island, this is in the middle of the River Seine near Verdon in Normandy. It was a successful attempt by Philip to gain acknowledgement that he was King over the lands in France that were owned by John, and that he as King of England did not have sovereignty over them.
This area is frequently referred to as the Angevin Empire, as the Kings of England were also Counts of Anjou. This arose from John’s father Henry II was father Geoffrey of Anjou married the Empress Matilda, daughter of Henry I. Indeed, they owned substantial areas of north-western France as by marriage they had accumulated Duchy of Normandy, and Count of Anjou. By Henry II’s marriage to Eleanor of Aquitaine that area also came into his control though was not affected by the treaty.
The only accession John was to gain from the Treaty was that Philip agreed he was the rightful King of England, rather than his nephew Arthur the son of his late elder brother, Geoffrey II of Brittany. However King Philip got John to agree that he would not support any rebellions started against the French King in Boulogne and Flanders, which had formerly been held by his predecessors. He also agreed that where he did own land within France he was under the rule of the King of France and it was not part of England.
One area not covered by the Treaty was Aquitaine. This is because Eleanor of Aquitaine, John’s mother and the reason why John held the title was still at this stage alive. However, what was to later course the problem was Brittany. Philip recognised John’s sovereignty over the area but demanded 20,000 marks for that privilege, even to this day some Bretons consider themselves Celtic along with some Cornish, Scots, Welsh and Irish.
Like many of the Treaties that were signed around that time, it was formalised also by a Royal marriage. In this case, Blanche (who was John’s niece) the daughter of Leonora and Alphonso VIII of Castile to Philip’s son who was to become Louis VIII of France. Sadly, the Treaty only lasted 2 years before Philip fell out with John for allegedly failing to acknowledge a summons and he also seized some of John’s lands in Normandy – strengthening the French crown. Further irony is that rather than helping seal a peace treaty, Louis VIII at one point invaded England and tried to claim John’s throne.