SERAPION, bishop of THMUS, saint. — The Syriac Calendar records a saint on 19 March; from there he passed into the *Martyrologium Hieronymianum* on the 21st of the same month; Eusebius mentions him (Hist. eccl., VI, 41, 8). Florus of Lyons in the 9th century, followed later by Ado, identified him with the S. of Thmus. The Roman Martyrology depends on the aforementioned interpolators.
S., initially a catechist at Alexandria, probably at the Didascalium, retired to the desert of Amun, became abbot of a colony of monks, and formed a close friendship with St Anthony the Abbot and St Athanasius. If the letter of Athanasius in which mention is made of a S. refers to our saint (PG 26, 1412 sq.), one must suppose that S. was already bishop of Thmus in Lower Egypt before 339. He was a learned man and, very likely, took part in the Council of Sardica (343) as a supporter of the aged Athanasius and of the Council of Nicaea against the Arians; for the same reason he was sent to the imperial court of Constantius II (c. 356); he seems to have died after 362. The title of “confessor” given him by St Jerome (PL 23, 699) appears to have been earned through exile, inflicted upon him by the Arian Ptolemy after the Council of Sardica.
Very little remains of S.’s theological output. A treatise against the Manichees is known under his name (G. Bardy, *La question des langues dans l’Église ancienne*, Paris 1948, p. 42), but like others of the period it was merely a collection of general, external information about the sect (cf. H.-Ch. Puech, *Le Manichéisme, son fondateur, sa doctrine*, Paris 1949, pp. 15–26); however, the arguments with which he combats the dualistic principle and the origin of evil are sound. His Trinitarian doctrine is among the simplest. The consubstantiality of Father and Son is designated by the imprecise term “homoiousios” rather than “homoousios”; even his Christological terminology is no more precise. This does not prejudice his orthodoxy and rather reflects the manner of expression of a bishop more concerned with pastoral than with polemical matters. Indeed, if he was sent to the Council of Sardica and if St Athanasius thought fit to address to him writings on the Holy Spirit (PG 26, 520–676), and if he was at first a catechist at Alexandria, one would conclude that he was capable of treating theological problems with greater respect for theological terminology. Indeed, according to others, St Athanasius held his friend’s learning in such high esteem that he submitted his own manuscripts to him for examination.
An Euchologion, or collection of 30 prayers, goes under S.’s name, but it cannot yet be critically established whether he is the author or merely a compiler: in this Euchologion there seem to be prayers dating from long before S. The first is an anaphora of particular theological as well as liturgical interest (P. Batiffol, *Etudes d’histoire et de théologie positive*, 3rd series: *L’Eucharistie*, 7th ed., Paris 1920, pp. 311–34).