Pope Zosimus (†418) was the bishop of Rome from 18 March 417 to his death. Zosimus took a decided part in the protracted dispute in Gaul as to the jurisdiction of the See of Arles over that of Vienne, giving energetic decisions in favour of the former, but without settling the controversy. He is venerated as a saint in the Eastern Orthodox Church as one of the pre-Schism "Orthodox Popes of Rome". His feast day is 27 December.
Pope Celestine I (†432) was the bishop of Rome from 10 September 422 to his death. Celestine's tenure was largely spent combatting various ideologies deemed heretical. He supported the mission of the Gallic bishops that sent Germanus of Auxerre in 429, to Britain to address Pelagianism, and later commissioned Palladius as bishop to the Scots of Ireland and northern Britain. In 430, he held a synod in Rome which condemned the apparent views of Nestorius. He is venerated as a saint in the Eastern Orthodox Church as one of the pre-Schism "Orthodox Popes of Rome". His feast day is 27 July (Catholic) and 8 April (Eastern Orthodox).