When the Arians had succeeded in having Eustathius deposed from Antioch and Athanasius from Alexandria, they turned their attention to Marcellus, bishop of Ancyra. Although less important as an ecclesiastic than the others, for his see was by no means as important as Antioch or Alexandria, Marcellus was important to the Arians as their most outspoken opponent; therefore he must be silenced as quickly as possible. In a lengthy treatise in reply to a Syntagma written by Asterius the Sophist, who had become the theological mouthpiece of the Arian party, Marcellus attacked the Arians–Eusebius of Nicomedia, Narcissus of Neronias, Paulinus of Tyre and, of course, Asterius himself–as well as Eusebius of Caesarea and Origen. Accused of Sabellianism at a synod at Constantinople in A.D. 336, Marcellus was deposed and went into exile in Rome. It appears that the synod deputed Eusebius of Caesarea to reply to Marcellus' views, which he did in two treatises, contra Marcellum and de Ecclesiastica Tkeologia.

Until very recently these treatises and Marcellus' place in the Arian controversy had received little notice. In 1902 F. Loofs drew attention to Marcellus as ‘one of the most interesting and instructive figures of the Arian controversy’. In 1939 H. Berkhof paid considerable attention to these treatises in his study of Eusebius' theology, and in 1940 the first full-scale monograph on Marcellus, by W. Gericke, was published. In Christ in Christian Tradition (1965), A. Grillmeier remedies a defect in his earlier German study of the history of christology in which he ignored Marcellus, by devoting a separate short section to his christology, as also does J. Liébaert (1966).