Pelagius (c. 360-420) was a British monk after whom a heresy was named.
Against the Pelagians
The last dialogue by Jerome (from 417) between Atticus, a Catholic, and Critobulus, a Heretic.
Bede's Ecclesiastical History of Britain
In Book I Section X of his history, Bede tells "How, in the reign of Arcadius, Pelagius, a Briton, insolently impugned the grace of God."
Ecole Glossary: Pelagius
Pelagius was assumed to be a Briton who, arriving in Rome in the 380's, attacked the moral laxness of the church. He came into conflict with Augustine for his view that human nature is inherently good and man's will is totally free.
Pelagianism emphasizes human free will as the decisive element in human perfectibility and minimizes or denies the need for divine grace and redemption.
Letter to the Bishop of Aquileia
Letter from Pope Leo on the dangerous Pelagian heresy.
Biographical article on the monk assumed to have come from Britain.
Pelagius and Pelagianism
Detailed entry on Pelagius from the Catholic Encyclopedia.
Preface to the Edinburgh Edition
Preface to a nineteenth century translation into English of five of fifteen treatise St. Augustine wrote against the Pelagian Heresy.