Local veneration of this depiction of the Assumption of the Virgin led to the building being designated a basilica minor by Pope Pius XII on May 23, 1954.

As the story goes, the knight was taken prisoner during the First Crusade and vowed to build a church in honor of Saint-Sauveur and the Holy Trinity if he ever returned home.

A charter from 1123, which established the division of the town between Olivier II and Alain de Dinan, the founder's nephews, implies that the building and its cemetery were already the property of the abbey of Saint-Jacut.

[4] Due to conflicts of jurisdiction arising between the two churches, it was decided that Saint-Sauveur would serve the southern part of the town, situated below the Rance bridge to the Jerzual gate.

These brotherhoods, under the patronage of saints such as Clément, Fiacre, Barbara, John the Apostle, Joseph, Crépin, Cecilia, Eligius, Laurent, Ascension, and Trinity, reached a total number of twelve by the 18th century.

[14] In 1851–1852, architect Hippolyte Béziers-Lafosse [fr] oversaw a restoration campaign that included rebuilding the west façade and south arm openings according to the design of the original bays.

[17] In February 2019, preventive archaeological excavations were carried out on the square situated in front of the church, as well as the Jardin Anglais, as part of a project to redevelop the area.

[19] The current structure of the building follows a Latin cross pattern and comprises a nave with a single aisle to the north, a projecting transept, and an apse marked by five radiating chapels.

The lower sections of the façade exhibit Romanesque architecture and are strongly influenced by edifices located south of the Loire, particularly those in Poitou and Saintonge.

The first voussoir depicts the elders of the Apocalypse and the labors of the months, while the second features stylized plant motifs with beaded ribbons that may be influenced by Byzantine styles.

After the installation of three contemporary sculptures, the capitals on the right arcade portray a dragon attacking a pilgrim, a depiction of lust highlighting devoured breasts, a deteriorated vegetal pattern, along with representations of animals including leaning birds, sphinxes, and confronted lions.

Consequently, the top section of the frontage is notably open, with a capacious and flamboyantly filled bay occupying the majority of the gable and providing illumination for the nave.

A molded cornice crowns the top of the wall, supported by intricately carved modillions featuring figures and ornamental elements like palmettes and acanthus leaves.

It extends three-sidedly from the wall and is topped by gables with sharp peaks, evocative of the radiating chapels of the Saint-Malo church, contemporaneously erected.

[30] The ornamentation incorporates flamboyant designs of curved arches, plant decorations, and prismatic volumes, as well as Renaissance features like flat carved rinceau and twisted columns.

The lower portions were constructed, but the upper sections were not necessary as counter-braces after the decision to replace stone vaulting with a paneled roof structure.

The nave and north aisle contain five bays and are connected by large arcades supported by strong columns, whose bases were removed when the floor was elevated in the eighteenth century.

[37] The ambulatory is vaulted with ogives, falling on nearly identical circular piers on either side of the circulation space, resulting in a significant plastic unity of the apse as a whole.

The square pilasters support the rib vaults in the sanctuary, constructed post-1570, and are connected to the cylindrical piers beneath the start of the large arches by scrollwork clasps.

The lower sections of the axis chapel showcase the same style of ornamentation, but with keystones carved with angels carrying shields and stylized floral designs.

The window portrays four Breton saints, Maturinus, Armel, Ivo, and Brioc, in the lower register, created in 1853 from drawings by Pierre Hawke.

These antique elements, potentially from the 13th century, were contributed to the church by a collector in the 1950s and were restored in 1959 by Hubert de Sainte-Marie [fr]'s workshop.

In addition, the third chapel of the ambulatory on the north side had a tympanum that housed a Christ-Judge dating back to the first half of the 16th century, which remained until 1923.

[40] The Basilica of Saint-Sauveur houses thirty-eight historic monuments, including paintings, altarpieces, sculptures, liturgical objects, and furnishings, all of which are listed or registered.

The plan underwent further revision by architect Jacques le Bonhomme from Saint-Malo prior to being entrusted to François Lamandé and Jean Lemonnier.

It depicts Éloi en évêque (Saint Eligius as a bishop in English), portrayed by painter and teacher Loyer from Rennes in 1817.

The church houses a stone bas-relief from the late 15th or early 16th century, portraying Saint Eustace with his children, one taken by a wolf and the other by a lion.

[63] Additionally, within the building is a reproduction of L'Ange gardien (The Guardian angel in English) by Simone Cantarini, which is based on a 19th-century engraving with an unknown origin.

They were relocated due to poor preservation conditions, specifically the climate, and a scenography project highlighting the military function of the Coëtquen tower, which was used for artillery.

The simultaneous management of these three projects enabled the organ builder to reduce production costs and to deliver instruments that, although practically mass-produced, were of a high standard in terms of pre-romantic aesthetics.