He conducted a famous controversy against the Pelagians, who denied original sin.

They were confronted with the argument from infant baptism.

"Why," it was said, "are infants baptized, if they need no change of nature ?" It would have been a triumphant answer could they have shown that it was an unscriptural practice, not countenanced by Christ or the apostles.

But Pelagius said, "Men slander me as though I denied baptism to infants, whereas I never heard of any one, Catholic or heretic, who denied baptism to infants." Pelagius and his friend Celestius, who was with him in the controversy, were born, the one in Britain, the other in Ireland.

They lived for some years in Rome, where they knew people from all parts of the world.