Zosimus, again doubting Pelagius' orthodoxy after renewed investigation at the council of Carthage in 418, reads his commentary on Romans; shocked by its doctrine, he commands Celestius to appear before him for examination.

Celestius flees Rome, thereby appearing self-condemned, and Zosimus issues the Epistola tractoria (“Epistolary Sermon”) that excommunicates Pelagius and Celestius and confirms the council's nine canons condemning their doctrine.

Pelagius, horrified by his excommunication, departs, probably for Egypt; nothing more is known of him after this date.

Even though Zosimus had confirmed Innocent's judgment, he disturbs the African episcopate in a new controversy by espousing the cause of a disreputable priest called Apiarius, who had been excommunicated by Bishop Urbanus of Sicca Veneria.

Defying African canon law, Zosimus dispatches legates to Africa with orders that include reorganizing the method of appeal between Africa and Rome and a threat to excommunicate Urbanus if he does not make amends with Apiarius.

Against the Pope's domination, certain Roman clergy appeal to the imperial court at Ravenna, the capital of the Western Empire, for which act Zosimus excommunicates them.

The case regarding Apiarius remains unsettled when, to the relief of both Africa and Gaul, Zosimus dies on December 26, 418.

When a majority of the Roman electors choose as pope the priest Boniface (believed to have been ordained by Damasus and to have served Innocent at Constantinople), a clerical faction simultaneously chooses his rival Eulalius, a deacon.

The two claims, and the resultant fifth schism, cause chaos in Rome.