The Norman invasions of the 9th century saw Tréguier and the cathedral ravaged so much that the then bishop, Monseigneur Gorennan, fled and had Tugdual's body moved to Chartres.

In 1345, the English invaded the area and used the cathedral as part of their garrison destroying much of the building in the process save for the tomb of Saint Yves which they left untouched.

In 1420, Duke Jean V had a chapel created so that he could be buried alongside Saint-Yves, the end of the 15th century saw the building of the cloisters, 1515 saw the construction of the choir's flying buttresses, and in 1648 the stalls which dated back to 1509 were restored.

The vaulted nave has seven crossings, and the sides comprise three levels starting with grand arcades, then a triforium and finally high windows.

The final and third tower is called the "Tour Neuve" and from this the cathedral spire rises, having been erected in 1787 to replace a bell-tower made from lead.

From the same standpoint of the Hôtel de Ville, one can see Francis Renaud's monument aux morts depicting a Trėguier woman grieving over the death of a loved one, a most poignant work.

The "porches des Cloches" is the main entrance to the building and here the trumeau is a statue of Notre Dame de la Clarté.

In the aisles to the left and right of the nave there are many enfeus or walled-up tombs of knights and clerics all sadly mutilated during the French revolution.

[2][3] Around the area of the "Tour des Cloches" is a wooden carved panel showing John of Patmos writing the apocalyptic Book of Revelation.

There is also a copy of a Murillo painting of Jesus and John the Baptist and a statue depicting Saint Yves between a poor and a rich man.

Three of the gisant given to the cathedral by the Musėe archėoloogique of Saint Brieuc are described in Emmanuelle Le Seac'h's book "Sculpteurs sur Pierre en Basse-Bretagne.

In 1632, a fire ravaged the sacristry, destroying many capes and chalices, and on 4 May 1794, the day Madame Taupin was guillotined in the main square, a battalion of the Revolutionary Army ran riot through the cathedral breaking statues, the tombs of Jean V and Saint Yves and damaging enfeu, porch statuary, wood carvings, furnishings and windows.

Jean V, Duke of Brittany had it seems made a promise in 1420 when a prisoner during the "War of Succession" that he would erect a monument to Saint-Yves and create a chapel dedicated to him.

The monument is located in the Duke's chapel lit by stained glass donated in 1937 by American, Belgian and French lawyers.

The windows of the Chapelle du Saint Sacrement depicting some events in Saint-Yves' life were placed here by the generosity of lawyers from various countries.

Saint-Yves died on 19 May 1303, at the manor of Kermartin in Minihy and on the day of his death he was carried by the priests of Tréguier to the cathedral surrounded by an enthusiastic crowd.

His mother Azo du Quinquis had a deep faith and told her son "Vivez, mons fils, de manière à devinir un saint!"

On 19 May each year, the Yves "pardon" is celebrated and the reliquary containing his skull is carried from the cathedral to Minihy by a procession of clerics and lawyers.

On the south face of the monument are depictions of Catel Autret, one of his friends Guiomar Morel, Charles de Blois in armour, Maurice, Archdeacn of Rennes and Catherine Héloury.

On the east face is a depiction of Clément VI who canonised Yves and Philippe V1 de Valois who initiated this canonization.

It dates to 1640 and is a copy of a Rubens painting which originally hung in the Église des Capucins in Aix-la-Chapelle but is now kept in the Rouen Museum of Art.

This 18th-century oil painting hangs in the cathedral and has the following inscription "Ceux qui prieront et adoreront le sacré Coeur de Jésus seront exaucez.

L'an 1720, les pestiférez de Marseille et d'ailleurs ayant dévotement invoqué le Sacré Coeur divin, la peste cessa aussitôt.

En faveur de ce miracle, l'an 1726, le pape Clément XI a accordé un bulle et des indulgences.

In Tréguier's Rue Saint-André and in a niche in the "Maison de Retraite Sœurs du Christ" is a statue of Saint-Tudwal dressed as a bishop and holding a book.

Thus the placing of Boucher's statue of Renan on Tréguier's cathedral square was interpreted as a challenge to Catholicism, and led to widespread protests, especially because the site was normally used for the temporary pulpit erected at the traditional Catholic festival of the "Pardon of Saint Yves".

The erection of this statue and the surrounding controversy led to the construction of the "Calvaire de Réparation" a "work of protest" designed by Yves Hernot This is a remarkable and dramatic Calvary.

The crosses and attendant figures are positioned on a pedestal which is decorated with a bas-relief depicting Saint Yves and below this is inscribed "vere hic homo filius dei erat/en gwirione an den ze e ca mab doue/cet homme etait vraiment le fils du dieu".

In the bas-relief, the Saint Yves relief is flanked by the coat of arms of Pope Pius X (right) and of Pierre-Marie-Frédéric Fallières, Bishop of Saint-Brieuc and Tréguier (left).

For those with an interest in Breton sculpture, the town hall at Tréguier is well worth a visit This painting by Joseph-Félix Bouchor depicts a view of the cathedral's cloisters.