Abstract: This chapter examines the moves toward a second Ecumenical Council in the years after the second depositions of Athanasius and Marcellus. Constantius’ brother, Constans, is presented as a central figure in the negotiations, perhaps from as early as 340. It is argued that the decisions of the Synod of Rome, here dated to Spring 341, were not intended to be binding on the East in the absence of any Eastern bishops, but merely addressed the local problem of whether or not to continue to treat Athanasius and Marcellus as bishops in the absence of convincing evidence that they had been validly deposed. The works written by Athanasius and Marcellus in Rome at this time, the First Oration against the Arians, the Letter to Julius, and probably On the Holy Church (De Sancta Ecclesia), are examined. It is argued that all draw on a statement agreed between the two concerning a heresy, which Athanasius calls the Arian heresy and Marcellus calls Ariomania. The signatories and documents of the Eastern and Western synods of Serdica are minutely examined, and argued to show that the two alliances were now in a process of realignment. Marcellus and Athanasius were in fundamental disagreement over whether or not to issue a statement adding to the Nicene Creed, and most of the Easterners were not in as intransigent a mood as the letter written in their name might suggest. Marcellus withdrew from public engagement with the controversy shortly afterwards to obviate the need to choose between a breach with Athanasius or with his own pupil Photinus of Sirmium. He died nearly 30 years later in communion with the former, without ever having condemned the latter.

Keywords: Ecumenical Council, Constantius, Constans, Synod of Rome, Julius, Athanasius, Serdica, Nicene Creed, Acacius of Caesarea, Photinus of Sirmium,