Helas saincte Marie et quelle
ces trois mors qui sot cy hideulx
mont fait meplre en gnt tristesse
de les vois ainxi piteulx.

Alas, St Mary! Who are these three corpses,
that are so hideous?
It breaks my heart
to see them thus piteous.

The legend which this illustrates is known as The Three Living and the Three Dead. The poem, dating from the Middle Ages, tells how three young princes, while out hunting, see three horrible corpses who give them a lecture on the perils of worldly success. There are over 90 known paintings of les Trois Morts et les Trois Vifs in French churches, including Kermaria, Plouha (Côtes-d’Armor); le Mont Saint Michel and Saint Georges de la Rivière (Manche); and Gonneville sur Honfleur (Calvados) in nearby Brittany and Normandy.

In the North Transept, a large mural has been cut in two by the arch which leads into the eastern part of the church. This shows that this was a solid wall at the time the mural was executed (about the second half of the 15th century) and that the chapel behind was entirely separate from the Church. All that left is St Barbara standing by her tower to the left, and a wing of the dragon that was slain by St Margaret to the right (Barbara and Margaret were often depicted together in this way). According to legend, Barbara, the hermit saint of Heliopolis (Egypt), was beheaded for her faith in the year 235 after having been shut up in a tower by her father Dioscorus. She became the patron saint of those in danger of sudden death by lightning, as her father was killed by a lightning bolt.

St Margaret of Antioch was imprisoned by Olybrius, governor of Antioch, and there tortured and finally eaten by a dragon. She made the sign of the Cross on its breast, which split in two, allowing her to burst out and escape safely. Her cult became very popular in France in the later Middle Ages, particularly among pregnant women, who prayed to her for safe delivery from the dangers of childbirth.

On the North Wall of the Nave is a representation of St Michael slaying the dragon. The Archangel is in complete armour except for his helmet. He is holding a broken hilt, the blade of which is near the Dragon, which he is stamping under his feet. The subject of this wall painting is said to have been due to a prioress who had connections with Le Mont St Michel. It is possible that when the Norman Louis de Brézé obtained possession of this part of the island by treachery for a short time in the 15th century, he had the work executed as a sign of victory. Judging by the lettering, these frescoes date from the second half of the 15th century, although some may be earlier, as the head-dresses and the armour of St Michael seem to belong to the 14th century.