The French had no option but to respond to so stark a challenge. On 19 May Rivière marched out of Hanoi to attack the Black Flags. His small force (around 450 men) advanced without proper precautions, and blundered into a well-prepared Black Flag ambush at Paper Bridge (Pont de Papier), a few miles to the west of Hanoi. In the Battle of Paper Bridge the French were enveloped on both wings, and were only with difficulty able to regroup and fall back to Hanoi. Like Francis Garnier ten years earlier, Rivière was killed in the battle. Liu had now taken the scalps of two French naval commanders in remarkably similar circumstances.