A Dictionary of Early Christian Biography 
Ammonius , a disciple of Pambo, and one of the most celebrated of the monks of Nitria. Being of unusual stature, he and his brothers Dioscorus, Eusebius, and Euthymius were called the Tall Brothers (Soz. Hist. viii. 12). Ammonius himself was distinguished by the epithet παρωής (Niceph. Hist. xi. 37), in consequence of having cut off one of his ears to escape being made a bishop (Pall. Hist. Laus. 12). In his youth he accompanied St. Athanasius to Rome (Socr. Hist. iv. 23; Pall. 12). He was a learned man, and could repeat, it is said, the O. and N. T. by heart, as well as passages from Origen and other Fathers (Pall. 12). He was banished to Diocaesarea in the persecution under Valens ( ib. 117). After being for some time high in favour with Theophilus of Alexandria, he and his brothers were accused by him of Origenism. Sozomen (viii. 12) and Nicephorus (xiii. 10) ascribe the accusation to personal animosity on the part of Theophilus. Socrates (vi. 7) explains the accusation as an attempt to divert from himself the odium which he had incurred as an Origenist. Jerome considers the accusation merited ( Ep. ad Alex. ). Driven from Egypt, the brothers took refuge first in Palestine (Niceph. xiii. 11) and afterwards at Constantinople, where they were well received by Chrysostom (viii. 13). There they were protected also by the favour of the Empress Eudoxia (Soz. viii. 13), and even satisfied Epiphanius of Salamis, who came to Constantinople at the instigation of Theophilus to convict them of heresy (viii. 15). At the synod "ad Quercum," held on the arrival of Theophilus, they were persuaded to submit to him, Ammonius being ill at the time. He died shortly afterwards. Perhaps this Ammonius is the author of the Institutiones Asceticae , of which 22 chapters are extant (Lambec. Biblioth. Vindob. iv. 155).
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
(1.) a disciple of Pambo, and one of the most celebrated of the monks of Nitria. He was distinguished by the epithet Παρωτής , in consequence of having cut off one of his ears to escape being made a bishop. In his youth he accompanied Athanasius to Rome; was a learned man, and is said to have been able to repeat the Old and New Tests. In the persecution under Valen's he was banished to Diocsesarea. After being in high favor for some time with Theophilus of Alexandria, he and his brothers were accused by him of Origenism; they first took refuge in Palestine (Niceph. 8, 13), and afterwards at Constantinople, where they were well received by Chrysostom. They were also protected by the favor of the empress Eudoxia (Sozom. 8, 13), and even satisfied Epiphanius of Salamis, who came to Constantinople at the instigation of Theophilus to convict them of heresy. Ammonins died soon after. He is perhaps the author of the Institutiones Asceticce, of which twenty-two chapters are extant. See Lambecius, Biblioth. Vindob. 4, 155.
(2.) An Egyptian bishop in the 4th century. At the age of seventeen he was induced, by hearing a sermon by Athanasius, to becomne a monk, not having as yet even been baptized, and retired to Taberna. After passing two years there, under Theodorus, and fourteen at Nitria, he was, as several other monks, apparently made bishop by Athanasius, and banished by George of Cappadocia. At the request of Theophilus, he wrote an account of St. Theodorus.
(3.) Bishop of Pacnemunis and, in part, of Elearchia in the 4th century. Having been a monk, he was made bishop by Alexander. He was sent with Serapion and other bishops on an embassy from Athanasius to Constantius; was banished shortly afterwards by the Arians; and returned in A.D. 362, in which year he was present at the councils of Alexandria and Sardica.
(4.) A solitary, near Canopus, in the 4th century. In the persecution by Valens he fled to Palestine, and thence to Sinai. There he was an eye- witness of the devastation of the monasteries and hermitages by the Saracens. Combefis supposes him, on returning to Egypt, to have been ordained presbyter by Peter, and thus identifies him with the Ammonius martyred with that bishop. He thence escaped to Memphis, where he made himself a cell. His narrative, in which he mentions also a similar devastation at the same time at Raithi, is edited in Greek, with Latin translation by Combefis.
is the name of several other saints:
(1) a martyr commemorated in Jerome's and Bede'a' martyrlogies on Jan. 31;
(2) an infant of Alexandria, commemorated in the old Roman martyrology on Feb. 12; (3) commemorated in Jerome's martyrology on Oct. 6.