After the decline of the Roman Empire, the further Christianization of Europe was to a large extent peaceful. However, encounters between Christians and Pagans were sometimes confrontational, and some Christian kings (Charlemagne, Olaf I of Norway) were known for their violence against pagans. In the late Middle Ages, the appearance of the Cathars and Bogomils in Europe laid the stage for the later witch-hunts. These (probably gnostic-influenced) sects were seen as heretics by the Catholic Church, and the Inquisition was established to counter them. In the case of the Cathars, the Albigensian Crusade violently suppressed them. In the Baltic countries, pagans were killed, subjugated or forcibly baptized.