The numbers were close enough that neither side could be confident. Louis of Nassau, William's brother, had crossed into the Spanish-held province of Groningen with 3,900 infantry. His younger brother Adolf rode at the head of 200 cavalry. Facing them was Johan de Ligne, Duke of Arenberg and Stadtholder of Friesland for the Spanish king, with 3,200 infantry and just 20 horse. Aremberg knew his cavalry was thin and chose caution. He pulled back and waited for reinforcements from the Count of Meghem, intending to face the Dutch rebels with overwhelming force. On the morning of 23 May, that plan came apart. Adolf's cavalry rode out in front of the rebel position - visible, taunting, apparently isolated - and Aremberg, against his own better instinct, took the bait.

The ground near the monastery of Heiligerlee was not what it appeared from the Spanish side. Louis had placed the bulk of his infantry where Aremberg could not see them. When the Spanish cavalry pursued Adolf's horsemen forward, the rebel infantry came up out of the dead ground and into their flank. The fighting that followed was short and brutal. Aremberg himself was killed. Roughly 460 Spanish soldiers died on the field. The rebels lost about 50 of their own, captured seven cannon, and walked off the heath with a victory that nobody in Brussels had thought possible. Among the fifty dead lay Adolf of Nassau.

Adolf's body was carried from the field by men who had ridden with him through the morning. He had no children, no political career, no record of military command before this campaign. What he had was a willingness to be the lure - to ride visible and exposed across a heath while three thousand infantry hid behind him, hoping the trick would hold. It held. He paid for it. The Dutch national anthem, written within a generation of his death, names him by his rank and his fate and not much else, because there was not much else to tell. The first verse of the Wilhelmus is sung at every state occasion in the Netherlands. The fourth verse is sung less often. But it is there, and it remembers him.

Heiligerlee was a triumph and a misdirection. Louis of Nassau had broken a Spanish army in open battle, but he had no cities, no siege equipment, no supply lines that could survive a serious counter-attack. The Duke of Alba, the Spanish king's most capable general, marched north with overwhelming force. Two months later, at the Battle of Jemmingen on 21 July, Alba destroyed what was left of Louis's army on the banks of the Ems. The first phase of the revolt was, by any military measure, a failure. The Spanish remained in control of the Netherlands. The rebellion would have to be rebuilt from almost nothing. But something had changed at Heiligerlee that no Spanish victory could undo. The Dutch had learned that the most feared army in Europe could be beaten in the field. The Eighty Years' War would run on that knowledge until 1648.

Heiligerlee today is a small village in the Oldambt municipality of eastern Groningen, surrounded by some of the flattest farmland in the country. A nineteenth-century monument marks the approximate site of the battle, and a small museum tells the story for visitors who find their way out from Winschoten. The monastery is gone. The heath has been drained and plowed for centuries. What remains is mostly the name itself, recurring at the moments when a country sings about who it is and how it began - in Friesland, in the battle, where Count Adolf died.