Pelagianism is not a doctrine about grace but an ascetic and reform movement. Pelagius was born in the early fourth century (ca. 350), perhaps in Britain. He came to Carthage in the late decades of the fourth century or the early decades of the fifth century. He adopted an ascetic life and gained a great reputation.
He devoted his zeal for the reform of behavior at his time and was hence regarded as a great moralist and religious teacher. He wrote many books on the subject of reform, emphasizing the “will” and underestimating “grace.” Pelagius sailed to Palestine where he met Jerome. His movement was adopted by many followers but was opposed by Augustine of Hippo. Pelagius returned to Carthage in 416.
Augustine wrote two letters to St. Cyril of Alexandria, wherein he explained the danger of this heresy. No reply from Cyril survived but one may assume that Augustine received a favorable answer, and so Pelagianism was condemned at the Council of Ephesus in 431 a.d. Nestorius in his conflict with St. Cyril took possession of some Pelegians.