Saint Valérien came in Tournus in the 2th century, in order to evangelize the population. Well, things didn't go according to plan! The saint was martyred and they founded an abbey where he was buried.
The abbey was dedicated, of course, to Valérien, then in the 9th century to saint Philibert (his relics were brought back in Tournus by monks from Vendée). Soon, our abbey became prosperous, but it was besieged by Hungarian invasions in 937, then a fire damaged it... then monks abandoned the place and moved in Auvergne.
They called back the former prior Etienne to manage the abbey: this one began a reconstruction, completed in the 12th century. But the abbot church was damaged during war of Religion, in 1562. Phew... it was saved during the Revolution.