He went to Rome where he was distressed by the moral decay of many Roman Christians. He blamed Rome's moral laxity on the doctrine of divine grace promulgated by Augustine.

Pelagius reasoned that if a man were not himself responsible for his good or evil deeds, there was nothing to restrain him from indulgence in sin.

Pelagius held that the human will is free to do good or evil, and that divine grace only facilitates what the will can do itself. After the fall of Rome to the Visigoths Pelagius went first to Africa, and then to Palestine.

After attacks from Augustine and Jerome, Pelagius was condemmed as a heretic.

From the Catholic Encyclopedia:
Biography