The Battle of St. Quentin in August 1557 had been a Spanish triumph and a French humiliation. Henry II of France spent the winter recruiting an army of revenge. He gave one column to the Duke of Nevers, asked the Ottoman Sultan for a fleet, and encouraged the Scots to threaten England's northern border. The Duke of Guise stole Calais back from the English in January 1558 - the loss that broke Mary I's heart, by her own confession - and then turned east to attack Spanish Luxembourg. Marshal de Thermes, meanwhile, was ordered to invade from the coast with 12,000 infantry, 2,000 cavalry, and a heavy train of artillery. He crossed the Aa River and aimed for Dunkirk, Nieuwpoort, and ultimately Brussels.

Lamoral, Count of Egmont moved faster than anyone expected. The Spanish governor of the Netherlands, Emmanuel Philibert of Savoy, gave him 15,000 infantry and 3,000 cavalry and turned him loose. De Thermes turned to find the Spanish army already on him - and his own position was a trap. The river Aa ran behind him, the sea was on his left, and on his right his own baggage train blocked any retreat. He arrayed his army in a double line: cavalry and artillery forward, infantry behind. Egmont deployed his force in a crescent: light cavalry on each flank, the Spanish, German, and Flemish foot in the centre. There would be no manoeuvre. There would only be the question of how badly the French could be broken.

The French fired first, and the cavalry of both armies tangled. The Spanish arquebusiers were the difference - better trained, better disciplined, and free to pick targets through the smoke. They peppered the French horse, then fired into the infantry sheltering behind the wagons until the ranks broke. Egmont led his cavalry directly at the centre. And then, off the dunes, Admiral Edward Clinton's Biscayan and English ships opened up on the French rear. The cannonade was unsuspected and devastating. The French line collapsed. Only 1,500 men escaped; the rest were killed or captured. Marshal de Thermes himself was taken prisoner. The lord of the river-mouth town was now a Spanish ward.

Coming after St. Quentin, Gravelines made the war financially unwinnable for France. Henry II opened negotiations, and in April 1559 he signed the Treaty of Cateau-Cambresis with Philip II. The clauses included two royal marriages designed to make the peace harder to reverse: Philip II - already widower of Mary Tudor, who had died the previous November - would marry Henry's daughter Elisabeth of Valois, and the Duke of Savoy would marry Henry's sister Margaret. The wedding tournament for Margaret of France would prove fatal: a lance shattered against Henry II's visor, and he died of his wound. The man who had launched the campaign of revenge did not live to see how much it had cost him.

Gravelines was the closing engagement of the long Italian Wars - the sixty-five-year contest between the Valois kings of France and the Habsburg emperors that had begun in 1494 with Charles VIII's march into Naples. Two generations of French dynastic ambition collapsed in the dunes north of Calais, on a stretch of coast that would be fought over again and again in the next four centuries. Egmont himself, the victor that day, would die under sentence eleven years later: arrested by the Duke of Alba and beheaded in Brussels for opposing Spanish repression in the Netherlands. The man who won Spain's last great victory in the Italian Wars would be killed for refusing to enforce the empire that victory had handed him.