Serapion or Sarapion (; ; early 4th century), known as Serapion of Nitria, Serapion of Thmuis or Serapion the Scholastic, was an early Christian monk and bishop of Thmuis in Lower Egypt. He is notable for fighting alongside Athanasius of Alexandria against Arianism.
Serapion is quoted in four sections of the Sayings of the Desert Fathers, where he is called Abba Serapion. He was given the title "The Angel of the Church of Thmuis" by Evagrius Ponticus in Gnostikos.
Before becoming a monk, Serapion was educated in Alexandria. He then became the abbot of the Monastery of Arsina (), which at one point held as many as eleven-thousand monks. He was given the title "the Great" by the early Christian historians Sozomen and Palladius.
As a monk, he was a companion and disciple of Anthony the Great, who at his deathbed bequeathed to him one of his two sheepskin cloaks (the other went to Athanasius).
In his later life , he was made the bishop of Thmuis (near Diospolis) where he served until his death . Jerome in his work On Illustrous Men noted that Serapion was given the apellation "Scholasticus" (the Scholastic) because of his meticulous scholarship. During his episcopate, he helped Athanasius fight against Arianism in Alexandria, and at his request, Athanasius wrote to him a series of three dogmatic letters on the theology of the Holy Spirit. These letters, which were written , are considered to be among the earliest Christian texts dedicated exclusively to the Holy Spirit. Serapion was one of the most trusted companions of Athanasius and even took care of his episcopal see during one of his exiles. In AD 353, Athanasius placed Serapion at the head of a delegation to Emperor Constantius II to plead guilty against the charges of the Arians. In 343, Serapion attended the Council of Serdica. Serapion was exiled by the Arians in AD 350, and died .
Serapion is said to have paid a prostitute, but instead of engaging in relations with her, prayed all night in front of her and eventually converted her to Christianity. She later became a nun at a monastery, practicing extreme ascetic labors. The same story also exists in a poetic Hymn of Praise in .
Only a few of Serapion's works have come down to us. The Sacramentary ascribed to him was not authored originally by him, but rather seems to be Serapion preserving the liturgical tradition of Thmuis. Fitschen discusses fragments of various writings in addition to the complete extant works listed below. Fitschen had concluded that Serapion did not author the Letter to the Monks but Herbel offers a correction on this front, arguing for Serapion's authorship. Both Herbel and Fitschen agree that Serapion did not author the Letter Concerning the Father and the Son, which is appended to the Sacramentary, and may date to the beginning of the Arian controversy. An Arabic Life of Anthony has also been attributed to Serapion but it is a much later redaction. It is possible that Serapion is the author of part or all of the LIfe of Anthony, credited to Athanasius, but Serapion's role as redactor and/or author warrants further exploration.