[1] [2] Jean Mabillon (1632–1707) conjectured that he had the same origins as Virgilius, Scottish or Irish, and that they came to Germany together to follow Boniface, "Apostle to the Germans.
"[3] A deacon named Sidonius appears as a witness in litigation concerning the Cella of S. Maximinus, against the priest Ursus, with whom Bishop Virgilius had a suit c. 748 (?).
[6] In a letter of 1 July 746, the pope notes that Sidonius and his associate Virgilius, apparently on instructions from Boniface, had been rebaptizing Christians who had been baptised by other priests with the formula, "Baptizo te in nomine Patria, et Filia, et Spirita sancta;" the pope points out that this was not introducing error or heresy, but mere ignorance of good Latin, and the rebaptizing by Sidonius and Virgilius should cease.
[9] Virgilius was accused of trying to drive a wedge between the legate Bishop Boniface and Duke Otilo of Bavaria, by blackening the reputation of Boniface, who had accused Virgilius of wandering away from Catholic doctrine (adversum te, pro eo quod confundebattur a te erroneum se esse a catholica doctrina).
[14] In a manuscript from the library of the monastery of Tergensee, compiled c. 1500,[15] the following is found: "Sidonius, secondus, anno Domini DCCXLV Archiepiscopus Laureacensis eligitur Pataviae et sedit annis XII."