The English had been here before. In 1492, Henry VII had laid siege to Boulogne's lower town with a force that achieved more theater than result. His son's ambitions ran larger. By 1543, Henry VIII had bound himself to Charles V, Holy Roman Emperor, in a new alliance against France - one that briefly overrode the Catholic emperor's distaste for the schismatic English king. France had been propping up Scotland against English aggression, and the Tudor crown wanted a continental foothold to punish Paris for it. The English had held Calais since 1347. Boulogne, twenty miles down the coast, was the natural extension. The army that gathered in the Pale of Calais in early 1544 was the largest English force assembled in living memory, and when it split in two, the Duke of Suffolk's wing marched directly south to the walls of Boulogne and opened bombardment on 19 July.

Henry arrived at the camp a few weeks into the siege and took personal command, an extraordinary act for a man whose ulcerated leg made every movement painful. The lower town - lightly fortified, vulnerable to artillery - fell quickly to sustained bombardment. Through August the guns hammered the upper town. By September the walls were breached. Only the central castle held out, its French garrison able to sweep the approaches with such withering fire that the English dared not assault it on foot. So they went underneath instead. Royal sappers dug tunnels beneath the castle's foundations, the medieval answer to a problem older than gunpowder, and on 13 September 1544 the French commander surrendered. Henry entered Boulogne five days later - the conquering king at last, having taken a continental town with his own banners flying overhead.

The triumph lasted exactly long enough for the news to reach Henry's allies. Within days, Charles V signed a separate peace with France, leaving England alone in the war it had joined to please him. The Dauphin's army turned its full weight on the captured town. Henry, his point made, sailed back to England at the end of September, ordering the Dukes of Norfolk and Suffolk to hold Boulogne to the last man. They promptly disobeyed: leaving roughly 4,000 men in the garrison, they marched the rest of the army back to Calais. On 9 October the French nearly took the town in a single assault - they were beaten back only because their own troops broke ranks to loot too early. The English clung on. For the next five years Boulogne became a fortress under permanent construction, a money pit consuming labor and stone in quantities no Tudor exchequer could comfortably bear.

What followed was an arms race in masonry. The English fortified a Roman lighthouse to the north, calling it the Old Man. They built a new fort between the lighthouse and the town and called it the Young Man. On a hill to the east they raised another - Boulemberg, the locals' name twisted into the English Mont Lambert. The French built rival forts south of the river Liane: Châtillon, Outreau, and eventually a chokepoint at Marquise that could blockade English supplies. Engineers like Richard Lee and Thomas Palmer crossed back and forth with instructions from the king. Of 1,200 English laborers sent over in January 1545, only 300 were still working by June - the rest had died or fallen sick. In 1549 the French finally tried to take Mont Lambert by night assault, set 200-rung scaling ladders against the walls at two in the morning, and discovered that their bribed insider had given the alarm. Two hundred French soldiers died on the slope. The women inside the fort were said to have saved the day.

Henry VIII died in January 1547 with Boulogne still in English hands. His son Edward VI inherited a war he could not afford. By 1550, with French pressure mounting and the Rough Wooing failing in Scotland, the Privy Council told the English captain at Boulogne to give it back. The imperial ambassador Simon Renard recorded that the captain accepted the order "with a sigh." Under the Treaty of Boulogne, signed in March 1550, France paid 400,000 crowns - a fifth of what the original Treaty of Camp had promised for an evacuation in 1554 - and the English departed. Henry II of France entered the town on 16 May and spent three days admiring the fortifications his enemies had built. He kept the Old Man, kept the Young Man, kept the star fort at Ambleteuse, and ordered the English mole rebuilt in the Roman style. Henry VIII's last continental conquest had lasted not quite six years.