[2] Concerning Alban of Mainz, he wrote: 21 June: The martyr Alban from [our] native Moguntia [Mainz], who during the reign of emperor Theodosius went forward from the island of Namsia with the saint Theonestus and Ursus, and reached Mediolanum [Milan], and from there he went out and, with the help of the Lord, he arrived in the provinces of Gaul, and stayed there in the Saviour's name, willing to suffer martyrdom in the service of God.

[note 1]The second substantial source is the Passio sancti Albani, an incomplete hagiography written in the 1060s or 1070s by schoolmaster Gozwin, who lamented that very little evidence about Alban had survived to his day.

[2][7] Gozwin's account is much longer and adds many elements not found in Rabanus' Martyrologium, including a prologue about the First Council of Nicaea (325) which condemned Arianism, that nevertheless persisted until Honorius and Arcadius succeeded Theodosius (395).

The most wise Ambrose teaches Theonestus and his disciples refined theology and sends them out to convert the 'Arian beasts' in Gaul and Germany.

[8] Heinz Thomas (1970) demonstrated how the Passio was written with a political goal: in the service of his lord Siegfried I, archbishop of Mainz, Gozwin presented the archbishop of Mainz as the primate of all Christians in Germany and Gaul, and framed the lives of Alban, Theonastus, Boniface and other Mainzer clerics in ways to prove this point.

[14] Some writers assert that the island of Namsia, also written Nausia, is to be equated with Naxos in the Aegean Sea,[5][14] while others state that they are not sure about this identification, or that they have no idea where to locate it because it doesn't seem to have existed.

Neither is it clear whether this Namsia was the birthplace of Alban, or (part of) the diocese of Theonistus, while others identify the latter as bishop of Philippi,[15] a city 450 kilometres north of Naxos.

Many writers doubt or outright reject Gozwin's assertion that Alban and Theonistus had been active in North Africa at the time of Vandal king Huneric on chronological grounds and the fact that Rabanus doesn't mention this episode.

[14] A timeline of Mainz constructed by Franz Falk (chaplain at Worms) for the Nassauische Annalen (1873) put the killing of bishop Aureus during the Hunnic sack of Mainz on 16 June 403, the killing of Alban by the Huns on 21 June 406, and the Crossing of the Rhine (by Alans and Gepids) on 31 December 406, based on Rabanus' Martyrologium, Gozwin's Passio, Prosper of Aquitaine's chronicle and Jerome's Epistola ad Ageruchiam.

[4] When the Diocese of Namur was created in 1559, it was expanded as St Aubin's Cathedral, which claims to possess relics of Alban of Mainz.