Thousands of Huguenots in France were massacred when, at the marriage of the Protestant Henry of Navarre and the sister of the Catholic King Charles IX, there was an assassination attempt on the Huguenot leader Coligny. The spooked King ordered influential Huguenots in Paris killed on Aug. 24, 1572; and the bloodbath soon spilled over into the French countryside, lasting into October. Pope Gregory XIII celebrated the mass slaughter with Te Deums and thanksgiving services in Rome.