Excerpts from Books and Wikipedia
"Where: Chateau Gaillard, at the confluence of the Rivers Seine and Gambon in northern France. . . . The castle not only guarded an important river crossing but also represented an insulting challenge to the French king, who wanted to regain lands lost to the English. . . . The French eventually managed to capture enough of the castle's defences to force a surrender. . . . It is likely that the humiliation of Chateau Gaillard played a part in the decision of the English barons to challenge King John." [Battles of the Medieval World] Chateau Gaillard … was built at great expense (L44,000) by Richard I of England in the 1190s. On cliffs above the Seine near Rouen, this key position in the defences for Normandy fell to king Philip II Augustus of France after a lengthy siege in 1204. [Cambridge Illustrated History of Warfare, p. 86]