He abandoned a career as a high-ranking government official to devote his formidable energy towards the promotion of the church and the protection of his "flock" in dangerous times, personally confronting, for instance, the barbarian king "Goar".

In Britain he is best remembered for his journey to combat Pelagianism in or around 429 AD, and the records of this visit provide valuable information on the state of post-Roman British society.

[1] At length he incurred the displeasure of the bishop, Saint Amator by hanging hunting trophies on a certain tree, which in earlier times had been the scene of pagan worship.

When the duke came to the church, Amator caused the doors to be barred and gave him the tonsure against his will, telling him to live as one destined to be his successor, and forthwith made him a deacon.

He distributed his goods among the poor, practised great austerities, and built a large monastery dedicated to Saints Cosmas and Damian on the banks of the Yonne, whither he was wont to retire in his spare moments.

[2] On the way to Britain they passed through Nanterre, where Germanus noticed in the crowd which met them a young girl, whom he bade live as one espoused to Christ, and who later became St. Geneviève of Paris.

Germanus led the native Britons to a victory against Pictish and Saxon raiders, at a mountainous site near a river, of which Mold in North Wales is the traditional location.

The sound echoed from the hills with a noise so loud that the barbarians, judging from the shout that they were facing a mighty army, flung down their arms and ran away, leaving behind their baggage and booty.

When Germanus awoke, he had the account written down in tituli, possibly to be engraved on the walls or illustrated placards at a church site, either in Britain, or in Auxerre.

Germanus then deposited some of the bones of continental saints in the basilica, and took a sample of the earth at the site of Alban's martyrdom, which still bore the marks of the martyr's blood.

Some have advanced arguments for the antiquity of the cult of Saint Alban (for example Martin Biddle[6]), while others suggest it was a rather artificial creation from the final years of Roman Britain, or soon after.

According to a legend recorded in the Historia Brittonum of circa 829 it is during this second visit, around 447, that Germanus is said to have condemned for incest and other crimes Guorthigern, identified with the 'Vortigern' of Welsh tradition.

[12][13] Saint Germanus' tomb continues to be venerated in the church of the Abbey of Saint-Germain d'Auxerre, which although now part of municipal museum remains open for worship at stated times.

The cult of Saint Germanus of Auxerre spread in northern France, hence the church Saint-Germain l'Auxerrois facing the Louvre in Paris.

He is associated with the church at Charonne in the east of Paris and the cult of Saint Genevieve (Genoveva) in Nanterre to the west of the city, both situated on the late Roman road network.