William the Conqueror was Duke of Normandy, in northern France, when he attacked and seized the crown of England in 1066. Throughout the rest of his reign, and of the six kings that followed, Normandy, while technically still owing its allegiance to France, was under English control. In order to keep that control, Richard I, known as the 'Lion-Heart', built a series of castles, including the imposing Château Gaillard.
Built in only one year - an amazingly short amount of time for a full-sized castle - Château Gaillard sat perched atop an ideal triangular outcropping of rock overlooking the Seine River Valley northwest of Paris. As this rock platform has cliffs on three sides and is therefore only approachable from the plateau to the south, it was an ideal site for a defensive fortification. Richard, who by all accounts was a gifted engineer, had his workers build a tower roughly the shape of a human ear on the very edge of the cliff. This tower - called the 'inner bailey' - was surrounded by a moat, spanned by only one small natural bridge. Around the moat was a second wall - the 'middle bailey' - ringed with towers. That, too, had one gate, and beyond that was the 'outer bailey', a third walled in courtyard, again ringed with towers. Although it cost Richard a fortune, the castle appeared impregnable. It was not.
Richard built fanatically, often joining the workmen personally, and the castle - which he called 'his daughter' - was completed in 1198. Unfortunately, only a few months later, Richard himself died after being shot by a crossbow during the siege of Chalus-Chabrol. He was succeeded by his brother John, who, in comparison to Richard, was more religious but had much less talent in the field of architecture and warfare. These factors combined to explain why John would order a hastily-built chapel within the middle bailey. Even more puzzling was why he would order a second construction adjacent to the chapel - a garderobe, or a castle latrine, with a sizeable opening in the middle bailey's wall.
John was a far less capable strategist than Richard was, and King Philip II of France took advantage of that weakness. Philip - supporting Richard and John's nephew Arthur's claim to the English throne - began a campaign to retake Normandy. Château Gaillard was the key to this campaign; and so Philip laid siege to the castle starting in September 1203. The French army approached from the only direction it could, and dug trenches and built walls of its own for protection. A daring nighttime relief mission from King John's forces failed miserably, as the foot troops arrived before the ships did, allowing the French to dismantle each element in turn.
By February 1204, King Philip's forces had managed to dig a tunnel under the outer bailey wall and collapse it, causing a breach through which their forces stormed. With this done, they were still faced with a problem: the middle bailey was reachable only by a drawbridge, which was up. The French siege, and the conquest of Normandy itself, would have likely come to a screeching halt, were it not for a foot soldier from Gascony named Snubby Bogis. Snubby - obviously a nickname - was creeping around the base of the middle bailey, not far from the steep cliff and plunge into the river, when he saw the window to the garderobe about three or four meters above ground. Realizing its implications, he got four of his companions to lift him up into the convenient hole in the wall. Emerging from the toilet, he dropped a rope and his friends climbed up after him. They crossed from the garderobe to the chapel, and found that it was locked from the outside. Thinking quickly, they banged on the door with their swords so hard that the English defenders thought the middle bailey had been broken and the whole army was upon them; they quickly set fire to the buildings and retreated to the inner bailey. Snubby and his friends then ran through the fire, opened the gates, and dropped the drawbridge, allowing the entire French force easy access.
The inner bailey was undermined shortly thereafter, as the natural bridge provided cover from the miners working in the moat. Château Gaillard fell to the French on March 8, and Normandy itself was back in undeniably French hands for the first time in almost 150 years - all thanks to an unguarded toilet.
Links and Sources:
"The Château Gaillard", by Thomas A. Janvier, from Harper's Magazine, volume 109, 1904.
Mediæval Military Architecture in England, Volume 1, by George Thomas Clark, Wyman and Sons, 1884.
Fighting Techniques of the Medieval World, AD 500 - AD 1500, by Matthew Bennett et. al., by Thomas Dunne Books, an imprint of St. Martin's Press, 2006