This text was written at a time of power struggle between Brittany and the County of Normandy against Francia as well as during canon law reforms by Roman emperors.

By this time, Mont Tombe was populated by religious devotees – hermits (probably some Celtic monks) supplied by the curé of Astériac, who took care of the site and led a contemplative life around some oratories, but there is no archeological evidence and no serious sources of that.

According to the legend, Aubert received, during his sleep, three times the order from Saint Michael to erect an oratory on the Mont Tombe.

The wealth and support that the Mont suddenly obtained from Rollo started to fundamentally affect its inhabitants, taking them away from their solitary, religious life.

Local nobles tried to obtain the favors of the Mont's religious inhabitants to spend it on meals, travels, and hunting in their company, which became their main occupation.

[8] After getting the approval from the local warlords and religious of the Norman abbeys, the monastery of Saint-Wandrille, Saint-Taurin-d’Évreux and Jumièges, Duke Richard I sent an officer and some soldiers to the Mont Saint Michel to announce his order: return to a religious life style and become a member of the Benedict order or leave the Mont.

Many underground crypts and chapels had to be built to compensate for this weight, forming the basis for the supportive upward structure that can be seen today.

Horrified by the exaction of his Brittany ally, Philippe-Auguste offered abbot Jourdain a grant for the construction of a new Gothic-style architectural set, which included the addition of the refectory and cloister.

The "Merveille", built in medieval Norman style, with a circular capital, some spandrels in Caen stone and some plant motifs, was completed in 1228.

Charles VI is credited with adding major fortifications to the abbey, building towers and successive courtyards, and strengthening the ramparts.

Mont Saint Michel's popularity and prestige as a center of pilgrimage waned with the Reformation, and by the time of the French Revolution there were scarcely any monks in residence.

The abbey was closed in 1791 and converted into a prison, initially to hold clerical opponents of the republican regime (up to 300 priests at one point).

In 1817, the numerous modifications of the structure by the prison administration led to the collapse of the hostelry built under Robert de Torigni.

Thanks to a corrupt system,[11] the richest prisoners could visit the Mont Saint Michel town, others could borrow books from the monks' scriptorium.

Up to 700 prisoners worked in a workshop set up in the abbey, making straw hats, which started a fire in 1834 and partially damaged it.

[12] After some higher-profile political prisoners were held there, such as Victor Dubourg de La Cassagne, Desforges, Martin Bernard, Armand Barbès and Auguste Blanqui, some influential figures, including Victor Hugo, launched a campaign to restore what was seen as a national architectural treasure, that led to its closure by Napoleon III in 1863.

[9] The prison was finally closed in 1863 and the abbey was rented by the bishop of Coutances starting that same year, until it was declared a monument historique in 1874.

In 1835, Viollet-le-Duc visited the Mont and later his students, Paul Gout and Édouard Corroyer (the famous Mère Poulard was his maid), were commissioned to restore it.

The archangel Saint Michel at the top of the spire (completed in 1898) was started in 1895 by the sculptor Emmanuel Frémiet at the "ateliers Monduit" that previously did some work for Viollet-le-Duc.

A cable car facility was installed but the abbey was otherwise kept intact, with the German Armistice Commission recognizing Mont-Saint-Michel's historical significance.

At the end of the summer a few stayed, led by Bruno de Senneville, from Bec Abbey, with the approval of the state, owner of the place.

In 1080, three levels were built to the North of Notre-Dame-Sous-Terre, including the "salle de l’Aquilon", which served as chaplaincy to host pilgrims, the monk promenade and a dormitory.

From 1154 to 1164 the abbot Robert of Torigni had a set of buildings added to the West and Southwest of the abbey containing lodgings for: the officiality, a new hostelry, an infirmary and the Saint-Étienne chapel.

The "Merveille", located to the North of the church-abbey, contains a cloister, a dining-hall, a study room and a chaplaincy with an ideal floor plan for going from one to the other.

The distinctive, regularly spaced abutments on the Merveille's outer walls reach to the top to reinforce the structure against any lateral forces imposed by the great weight of its towering upper levels.

Abbot Richard Turstin built, on the east side, the Guards room (that became the abbey entrance) and a new officiality, where judicial decisions were made (1257).

During the medieval period, pilgrims visiting the abbey walked from Italy, Germany, and England as well as other parts of France.

Ten hiking trails have been created that enable pilgrims from various European countries to retrace the path their ancestors may have taken during a medieval pilgrimage.