December 17 (Eastern Orthodox liturgics) - Wikipedia
https://en.wikipedia.org/wiki/December_17_(Eastern_Orthodox_liturgics)
Dec. 16 - Eastern Orthodox Church calendar - Dec. 18. All fixed commemorations below ... brother of Saint Cadfan (6th century); Saint Briarch, born in Ireland, became a monk in Wales with St Tudwal, whom he accompanied to Brittany, built ...
December - Orthodox England
orthodoxengland.org.uk/stddec.htm
Diodorus, Marianus and Companions Dec 1 + 283. Martyrs in .... 6th cent. A noble in Wales, he ended his life as a monk with St Illtyd. ..... Briarch Dec 17 + c 627.