Orthodox Saints of the Pre-Schism See of Rome
10th January
AGATHO, Pope of Rome from 678 until his repose in 681. Originally from Sicily, St. Agatho was a businessman for most of his life, who then received monastic tonsure, and prior to his election to the papacy he was the treasurer of the church of Rome. St. Agatho was elected seventy-ninth Pope of Rome in 678. As Pope, St. Agatho worked to resolve the conflict between SS. Wilfrid (12th October) and Theodore (19th September) over the boundaries of the See of York. He also fought against the Monothelite heresy, and his writings played a crucial role in formulating the decision of the Sixth Œcumenical Council in Constantinople in 680 against Monothelitism. St. Agatho reposed in 681.
ARCONTIUS, (Eighth or Ninth Century), a Bishop of Viviers who, local legend states, was beheaded by a mob of Viviers’ citizens. His feast is observed in the Diocese of Viviers on 19th January.
DERMOT (DIARMIS, DIARMAID), (sixth century), Known from his earliest years for his sanctity, he was the spiritual father and teacher of St. Kieran of Clonmacnoise (9th September). St. Dermot went on to found, and serve as first abbot of a monastery on Innis-Clotran Island (Inchcleraun), Co. Longford Ireland.
JOHN CAMILLUS the GOOD, consecrated thirty-seventh Bishop of Milan in 641, St. John Camillus was the first Bishop of Milan in eighty years able to reside in Milan following the Lombard invasion. He was an indefatigable defender of orthodoxy against the heresies of Arianism and Monothelitism. St. John Camillus reposed circa 660.
PETER ORSEOLO (URSEOLUS), a Venetian who served as Admiral of the Venetian fleet and then Doge of Venice. After two years as Doge he abandoned the world and entered the Abbey of Saint-Michel-de-Cuxa in the Pyrenees, where he received monastic tonsure. There he was a disciple of St. Romuald (19th June), who ultimately advised St. Peter to live as a hermit, which he did, until his repose in 987.
PETRONIUS, born in Avignon, St. Petronius received monastic tonsure at Lérins Abbey, and finally served as second (or possibly third) Bishop of Die from circa 456 until his repose circa 463.
SETHRID (SÆTHRYTH), a stepdaughter of Anna, King of East Anglia, and half-sister of SS. Etheldred (Audrey) (23rd June) and Ethelburgh (7th July). St. Sethrid received monastic tonsure at the Abbey of Notre-Dame de Faremoutiers under St. Burgundofara (3rd April), whom she succeeded as abbess. St. Sethrid reposed circa 660.
THOMIAN (TÓMMÉNE, TOIMEN), St. Thomian was the seventeenth Archbishop of Armagh, from circa 623 until his repose circa 660. Always renowned for his great sanctity of life, he is also remembered for a letter he and several of his fellow bishops in Ulster wrote to Rome seeking the Pope's advice on the Paschal Controversy.
Prior to the Schism the Patriarchate of Rome was Orthodox, and fully in communion with the Orthodox Church. As Saint John of Shanghai and San Francisco +1966 said “The West was Orthodox for a thousand years, and her venerable Liturgy is far older than any of her heresies”.
Details of British Saints excerpted from Orthodox Saints of the British Isles.
Details of continental saints from these sources.
In many cases there are several spelling versions of the names of saints from the British Isles. I use the Oxford Dictionary of National Biography version as the primary version with the more prevalent version in parenthesis e.g. Ceadda (Chad) of Lichfield.