According to Alban Butler, in his youth, Tigernach of Clones "...was carried away by pirates into Britain, and fell into the hands of a British king, who being taken with his virtue, placed him in the monastery of Rosnat.
We are inclined to agree with Skene that it was rather the celebrated monastery known as Candida Casa, or Whithern, founded by St. Ninian at the extremity of the peninsula of Galloway.
Wilson says that the development of the cult of Ninian after publication of Bede's Ecclesiastical History caused later editors of vita pertaining to Irish saints who trained in Britain, to identify the unknown Rosnat and its abbot Macannus with Candida Casa and Ninnian.
[8] Irish hagiographer and historian John Colgan believed Rosnat or "Alba" was Bangor-on-Dee, founded about AD 560 by Saint Dunod from the preface "ban", meaning "white".
"Dr Breeze, writing in the Welsh Journal of Religious History (Vol 7), is convinced that “Rosnat was surely in Cornwall, near Truro”.