Château Gaillard was a strategic fortress built by King Richard I of England in 1196 to guard the Seine valley against any incursions by the French. Its construction represented a significant enhancement of England's military capabilities on the continent. Following Richard's death, his brother King John faced numerous challenges, both domestically and abroad. King Philip II Augustus of France capitalized on these weaknesses, recognizing the importance of Château Gaillard in maintaining control over Normandy and centralizing his power in France.

The siege began in early 1204 when Philip II ordered his forces to surround the fortress. The castle's defenses, designed by Richard, were formidable; however, the French forces employed innovative siege tactics, including the use of siege engines and a prolonged blockade. Despite fierce resistance from the English garrison, the relentless French assault and dwindling supplies ultimately led to the castle's surrender. The fall of Château Gaillard effectively signaled the end of English rule in Normandy, as King John's inability to defend his territories against Philip's forces severely diminished his authority.

The aftermath of this siege had profound implications for both French and English politics. With Château Gaillard in French hands, Philip II reclaimed Normandy, further consolidating his power. This victory not only diminished King John's influence but also invigorated French nationalism, leading to greater territorial ambitions in the years that followed. The battle over this stronghold was critical in shaping the relationships between England and France, leading to a long-standing rivalry that would manifest in later conflicts like the Hundred Years' War.