Caelestius was a disciple of Pelagius, involved in the discussions over the free will, original sin, and grace at the beginning of the fifth century in Rome, North Africa, and Palestine. He was ordained a presbyter between 411 and 416 during his travel to the East (see [497], [503] and [953]). He went back to Rome in 417 after the election of Zosimus as the bishop of Rome. There he appealed to Zosimus, asking him to judge his writings and opinions against those who were accusing him of heresy [1467]. Zosimus interrogated Caelestius, and did not found him guilty, instead he condemned his accusers, Heros and Lazarus. He also summoned other accusers, mainly Paulinus, deacon of Milan, who at the council in Carthage in 411 had accused Caelestius of heresy, to Rome. For the response of Paulinus to Zosimus see [1497]. The present letter is the last papal response on the case and was sent on 18 March 418 (received in Africa on 29 April).