The barbarian invasions were presaged by a pillaging and burning in 276, from which Roman Vasio recovered, but in the fifth century the benches of the theatre began to be reused as Christian tombstones. Vaison belonged the Burgundians, was taken by the Ostrogoths in 527, then by Clotaire I, King of the Franks in 545, and became part of Provence The disputes which broke out in the twelfth century between the counts of Provence, who had refortified the ancient "upper town" and the bishops, each of whom were in possession of half the town, were injurious to its prosperity; they were ended by a treaty negotiated in 1251 by the future pope Clement IV, a native of Saint-Gilles-du-Gard.
At disturbed times of the Middle Ages, the inhabitants emigrated to the higher ground on the left bank of Ouvèze, with the shelter of the ramparts and a strong castle. From the eighteenth century most of the population had moved back down to the plains by the river.
St. Albinus (d. 262) was incorrectly placed by the Carthusian Polycarpe de la Riviere among the bishops of Vaison. The oldest historical bishop of the see was Daphnus, who assisted at the Council of Arles in 314. Others were St. Quinidius (Quenin, 556-79), who valiantly resisted the claims of the patricius Mummolus, conqueror of the Lombards; Joseph-Marie de Suares (1633-66), who died in Rome while filling the office of librarian of the Vatican, and who left numerous works. St. Rusticala (b. at Vaison, 551; d. 628) was abbess of the monastery of St. Caesarius at Arles. Two rather important councils as regards Gallican ecclesiastical discipline were held at Vaison in 442 and 529, the latter under the presidency of St. Caesarius.
The recovery of Roman Vaison started about 1907 was for a generation under the control of Canon Joseph Sautel (died 1955), whose concern was the recovery of the 'best period' of the first century CE, in pursuit of which he ignored and eliminated later remains, with picturesque and highly visitable restorations. Its chief modern interpreter has been Christian Goudineau.
One of the most interesting aspects of the town is its geography, and its Roman ruins. The Roman ruins and the modern town are in the valley on the banks of the river Ouvèze which is crossed by an ancient bridge from the first century. The medieval town is high on the rocky cliff. The valley floor was safe from attack in Roman and modern times. In the Middle Ages attacks were frequent, and the town retreated up-hill to a more defensible position.
The apse of the Church of St. Quenin, dedicated to Saint Quinidius, seems to date from the eighth century; it is one of the oldest in France. As a whole the cathedral dates from the 11th century, but the apse and the apsidal chapels are from the Merovingian period.