The siege of Breteuil was the investment of the Norman town of Breteuil, held by partisans of Charles II, King of Navarre, by French forces. It lasted from April to about 20 August 1356. It was interrupted on 5 July when a small English army commanded by Henry, Earl of Lancaster relieved and resupplied it. The French king, John II, attempted to bring Lancaster to battle with the much larger French royal army, but Lancaster marched away and the attempt failed. John then renewed the siege of Breteuil.