Tournus Abbey has never been analysed otherwise than by the formalist method. A change in approach will permit to uncover new secrets relating to this monument. A study of the political context – not an easy matter – reveals a very close relationship between Italy and Burgundy around the year 1000, and the twinning of the two construction sites: of Saint-Bénigne in Dijon and that of Saint-Philibert in Tournus.

Almost ignored by historians, the putsch in 1002 at least partially explains the ‘white mantle of churches’, a vast reconstruction movement which Rudolf Glaber believed to have started in that year. Dijon and Tournus are the chefs-d’oeuvre of a co-ordinated wave of construction with a focus on political separatism.

The evocation of Constantine’s accession to power permeates the whole conception of galilee. This is the only part of the abbatial structure analysed here. Several monuments constructed between 310 and 320 served as inspiration to the architect; they are here reproduced in a reduced size. This evocation seems to be connected to Constantine’s Vision of the Cross, an event which, according to an ancient tradition, took place in the Tournus area. This episode is certainly related to the life of Saint Valerien, the evangelist of Tournus, in the second century. This is the first time that such a long legitimising tradition has been described.

The study also reveals that the architect of this abbey can be no other than Guillaume de Volpiano, and the commissioner Otte-Guillaume, duke of Burgundy, his second cousin.