What role did Constantine I play in disputes between Christian groups such as the Donatists?

Constantine I viewed religious schisms as a threat to the stability of the Roman Empire, believing that a divided church would offend the Christian God and invite divine vengeance. He considered it his imperial duty to resolve these conflicts and propagate the true religion, famously claiming to be the "bishop of those outside the church".12

Regarding the Donatist controversy in North Africa, Constantine took several direct actions:

• Arbitration: He initially ordered an investigation into the dispute, leading to a commission of bishops in 313 that ruled against the Donatists.3
• Council of Arles: When the Donatists appealed this decision, Constantine convened the Council of Arles in 314, the first representative meeting of Western bishops, which also condemned the group.24
• Final Judgment: After further appeals, Constantine issued a final decision in favor of the Catholic bishop Caecilian in 316.3
• Enforcement and Toleration: He attempted to suppress the movement through persecution between 317 and 321, but eventually granted the Donatists grudging toleration in 321 after the measures failed to end the schism.3