The Battle of Sandwich was fought off the Kent coast in 1217. This battle brought an end to the career of Eustace the Monk. Eustace seems to have been one of those characters of history who lived colourful lives and are fun to read about, but might not have been so nice to meet in person. Eustace may have started out as a peaceful monk but he soon became a pirate and a mercenary roaming up and down the English Channel. He operated at various times in the pay of both Philip II, King of France and his rival King John of England.
Eustace was born around 1170, so he was roughly contemporary within Robin Hood. However while Robin Hood was almost certainly fictional, there is plenty of evidence that Eustace really existed. From 1205 he worked intermittently for both kings who were at almost constantly at war with each other. He was obviously quite useful to King John who put him in charge of a fleet of 30 ships for operations against the Normandy coast. Indeed John eventually pardoned him when Eustace exceeded his instructions and raided some villages on the English coast as well.
By 1217 however Eustace had switched sides and was working for the French. He was carrying war supplies for King Phillip when he was intercepted off Sandwich by a fleet that had been raised in the Cinque Ports. His ships were boarded by the English and defeated in battle. Naval warfare in those days was fought by bringing the ships alongside each other, so that armed men could jump across. It is said that on this occasion the English sprayed lime powder from upwind to blind the French crews before boarding. Eustace was found hiding in the bilges of his ship. He offered to pay a huge ransom, but was so despised by the English sailors that he was executed on board.
Eustace may seem a minor figure from a long time ago, but he has probably left his mark on the modern world. The Channel Islands were part of the Duchy of Normandy even before William the Conqueror invaded in 1066 and when King John lost his lands in Normandy in 1204 the Channel Islands might too have reverted to French ownership. However Eustace made his base in the Islands (principally Sark and Guernsey) to resupply and repair his ships while working for King John. He operated from the Islands while raiding the Normandy coast.
Following the defeat of Eustace and the French at the battle of Sandwich, the English successfully retained the Channel Islands as a possession of the English crown, as they remain to this day.