Aubert was born about the year 660 in the country around Avranches, in what is now the Manche of Normandy — tradition names Genêts or Huisnes-sur-Mer as his birthplace — into the noble family of the lords of Genêts, in the days of the Frankish king Childebert III. He was given an unusually thorough education for his time. When his relatives died, he did not cling to the lands and goods that fell to him: he distributed his inheritance to the poor and gave himself to the service of the altar, receiving priestly ordination. Poverty freely chosen was the door through which he entered his life's work.
His reputation for wisdom, piety, and open-handed charity spread through the region, so that when the see of Avranches fell vacant he was chosen bishop — by acclamation, according to tradition — in the year 704. As pastor he was known above all for mercy to the needy, and he kept the habit of withdrawing to a lonely rock in the bay, Mont Tombe, where since the sixth century hermits had lived, in order to give himself to prayer and meditation.
The hagiographic tradition preserved in the ninth-century Revelatio ecclesiae sancti Michaelis in monte Tumba, written by a canon of Avranches or of the Mount, tells that Aubert delivered his people from a dragon that was ravaging their herds: making the sign of the cross and casting his stole over the beast, he commanded it to go down into the sea and never appear again. The same tradition relates that he witnessed a combat between the Archangel Michael and the dragon, begun on Mont-Dol and finished on Mont Tombe, and that on the very place where the evil one was overcome the Archangel bade him raise a sanctuary, after the pattern of Monte Gargano in Italy, where Michael had been honoured since the fifth century.
So in the year 708, while Aubert slept after prayer, Saint Michael appeared to him and commanded him to build a church in his honour on the tidal rock at the mouth of the Couesnon. The bishop hesitated: the crag was arid and solitary, covered with brambles, inhabited only by wild beasts and a few hermits, and he feared the vision might be a deception of the devil. The Archangel came a second time, and still Aubert delayed. At the third apparition Michael pressed his finger firmly upon the bishop's head, leaving a mark; Aubert awoke with the hollow in his skull and understood that the command was true.
Providential signs then guided the work, as the tradition tells. One September morning a ring of dew showed him the round shape the oratory should have; a bull strangely tethered on the rock marked out the site; a spring of fresh water broke from the hard stone — the place is still called the Fontaine Saint-Aubert. A pagan cult stone, probably a menhir, resisted the efforts of a neighbouring farmer named Bain and his twelve sons, until Aubert set the farmer's youngest child, whom he held in his arms, against it, and the stone gave way. After another dream, Aubert sent two monks to the sanctuary of Monte Gargano in Italy to bring back relics of the Archangel. Then, on 16 October 709, the bishop dedicated the church and installed there a chapter of twelve canons. Mont Tombe lost its old name and became Mont-Saint-Michel-au-péril-de-la-Mer: the abbey was born, and in later centuries the canons gave way to Benedictine monks.
Aubert died about the year 725, on 18 June according to one tradition, at Avranches. As he had desired, his body was carried to the Mount and laid in the choir of the church he had raised, his head toward the altar, while the canons kept his skull and his right arm as relics. When Benedictines replaced the clerics in 966, the canon Bernier is said to have hidden his bones near the primitive oratory, perhaps to save them from the Northmen. The Introductio monachorum and the De translatione et miraculis beati Autberti recount how, under Abbot Hildebert I, between 1009 and 1023 — the recognition of the body is dated to 1012 — the monks found in a hermit's hut a skeleton whose skull bore a hole, and the relics were solemnly enshrined. From then on pilgrims venerated the "chief of Saint Aubert" as bearing the print of the Archangel's finger.
In 1792, when revolutionary fury threatened the treasures of the Church, a physician of Avranches, Louis-Julien Guérin, obtained the skull on the pretext of scientific study and, when peace returned, restored it to the clergy; the reliquary of the arm had disappeared. Since 1856 the relic has been kept in the treasury of the basilica of Saint-Gervais-et-Saint-Protais at Avranches, where it may still be seen: an amber-coloured skull with a nearly circular perforation on the right parietal bone. Modern examinations have proposed a cyst or a trepanation as the natural cause of the opening, and a radiocarbon dating carried out in 2019 placed the skull between 662 and 770 — a date wholly compatible with the tradition of the Mount's foundation. Whatever science concludes about the bone, the Church honours the bishop who obeyed at last, and whose obedience gave Christendom one of its greatest sanctuaries of Saint Michael. His feast is kept on 10 September.
May Saint Aubert obtain for us the grace to stop hesitating before what God asks, and to practise today, as he did, a generous charity that strips itself of its own goods for the poor.