At the time of the Siege of Rouen (July 1418 – January 1419), the city had a population of 70,000, making it one of the leading cities in France, and its capture crucial to the Normandy campaign during the Hundred Years' War. From about 1415, Rouen had been strengthened and reinforced by the French and it was the most formidably defended place that the invaders had yet faced. After the city fell, many of the inhabitants were so sick of both the Duke of Burgundy and the dauphin that they swore allegiance to Henry.