It was an assassination attempt against Gaspard de Coligny that triggered the violence. Since the last edict of pacification, the admiral had been a member of the King's Council, where he had considerable influence. His idea of French support for Protestant uprisings in the Netherlands caused alarm in Catholic circles and worried Catherine de Médicis.
Returning home on the morning of 22 August 1572, Coligny was hit by a volley of bullets that tore a finger from his right hand and shattered his left elbow. The Huguenots immediately suspected the Guise family and the queen mother's entourage. They felt trapped in a city that hated them, and where they feared double-dealing by the king. Some fled, but most remained, trusting in the words of Charles IX , who promised to find "the guilty party, the accomplices and the rabble-rousers."
At the same time, Catherine de Médicis and her advisers made a decision. In order to avoid retaliation by the furious Huguenots, she drew up a list of those who should die. Henri de Condé and Henri de Navarre were not on the list, no doubt because they were princes of the blood. After some hesitation, the king agreed. He was won over by proscriptive arguments – greater troubles could be avoided by killing a few leaders.
The instigators had not anticipated the pent-up rage and hatred of the Parisians that would explode in the early hours of 24 August 1572 – St Bartholomew's Day – and that would degenerate into a widespread massacre of any Protestant within reach. For three days, the capital city was the scene of a vast and bloody manhunt. Neighbours, friends and enemies alike were hunted down and killed by the sword, burnt or drowned. The eradication of heresy, so often called for by fanatical preachers, was finally underway. Coligny was one of the first to die. He was dragged from his bed, beaten and killed. His body was thrown out a window, and was then cut into pieces and dragged through the streets. The violence, which claimed between 2,000 and 3,000 victims, spread like wildfire throughout France – Huguenots were slain in a number of other cities, including Bordeaux and Toulouse, where the killings ended in October 1572.
Henri de Navarre witnessed the slaughter of the companions who had accompanied him to Paris, powerless to act. He was fetched from his chambers on the night of the 23rd and taken to the king's apartments, where he found his cousin Condé. He would never forget that night, and how he saw and heard his friends being killed in the Cour Carrée of the Louvre, in a paroxysm of senseless violence.