signalled the start of a wave of violence against the Huguenots. After a successful Spanish attack on his army, William had to flee and he retreated to Enkhuizen, in Holland. The Spanish then organised countermeasures, and sacked several rebel cities, sometimes massacring their inhabitants, such as in Mechelen or Zutphen. They had more trouble with the cities in Holland, where they took Haarlem after seven months and a loss of 8,000 soldiers, and they had to break off their siege of Alkmaar. In 1573, William joined the Calvinist Church. He appointed a Calvinist theologian, Jean Taffin (1573–1581) as his court preacher. Taffin was later joined by Pierre Loyseleur de Villiers (1577–1584), who also became an important political advisor to the prince. In 1574, William's armies won several minor battles, including several naval encounters. The Spanish, led by Don Luis de Zúñiga y Requesens since Philip replaced Alba in 1573, also had their successes. Their decisive victory in the Battle of Mookerheyde in the south east, on the Meuse embankment, on 14 April cost the lives of two of William's brothers, Louis and Henry. Requesens's armies also besieged the city of Leiden. They broke off their siege when nearby dykes were breached by the Dutch. William was content with the victory, and established the University of Leiden, the first university in the Northern Provinces. William married for the third time on 24 April 1575 to Charlotte de Bourbon-Montpensier, a former French nun, who was also popular with the public, although less so with the Catholic faction. They had six daughters. The marriage, which seems to have been a love match on both sides, was happy. After failed peace negotiations in Breda in 1575, the war continued. The situation improved for the rebels when Don Requesens died unexpectedly in March 1576, and a large group of Spanish soldiers, not having received their salary in months, mutinied in November of that year and unleashed the "Spanish Fury" on Antwerp, sacking the city in what became a tremendous propaganda coup for the rebels. While the new governor, Don Juan of Austria, was en route, William of Orange got most of the provinces and cities to sign the Pacification of Ghent, in which they declared themselves ready to fight for the expulsion of Spanish troops together. However, he failed to achieve unity in matters of religion. Catholic cities and provinces would not allow freedom for