12 April 352
The immediate successor of Pope Silvester, Arcus, ruled the Roman Church for only a very short period — from 18 January to 7 October, 336 — and after his death the papal chair remained vacant for four months. What occasioned this comparatively long vacancy is unknown. On 6 Feb., 337, Julius, son of Rustics and a native of Rome, was elected pope. His pontificate is chiefly celebrated for his judicious and firm intervention in the Arian controversies, about which we have abundant sources of information. After the death of Constantine the Great (22 May, 337), his son Constantine II, Governor of Gaul, permitted the exiled Athanasius to return to his See of Alexandria (see ATHANASIUS). The Arians in Egypt, however, set up a rival bishop in the person of Pistus, and sent an embassy to Julius asking him to admit Pistus into communion with Rome, and delivering to the pope the decisions of the Council of Tyre (335) to prove that Athanasius had been validly deposed. On his side Athanasius likewise sent envoys to Rome to deliver to Julius a synodal letter of the Egyptian bishops, containing a complete justification of their patriarch. On the arrival of the Athanasian envoys in Rome, Macarius, the head of the Arian representatives, left the city; the two remaining Arian envoys, with the Athanasian deputies, were summoned by Pope Julius. The Arian envoys now begged the pope to assemble a great synod before which both parties should present their case for decision.
(Taken From Catholic Encyclopedia)