With the exception of a few, we may take it that many embraced Christianity as a matter of compulsion or for expediency's sake, for in those days of hard knocks it was hardly likely that any mass of ignorant peasants would comprehend anything but the most stringent measures. The transition from heathen darkness to the light of Christianity must have meant a severe initiation to two-thirds of the population of Exeter at the time of Athelstan's accession. He came westward about the year 926 and found the Britons and Saxons living amicably and enjoying equal rights. The city had by them already been called Exenceaster, that is, the "cester" or fortified town on the "Exe." Athelstan augmented the number of religious institutions by the foundation of a Benedictine monastery. The building was dedicated to St. Peter, the establishment of which there seems no reason to doubt gave birth eventually to the present cathedral. Besides this he materially increased the importance of the town by appointing two mints and erecting regular fortifications with towers and a wall of hewn stone. Athelstan's monastery was destroyed by the Danes. King Edgar in 968 restored it, and appointed Sydemann to the Abbacy, as it then became. Ultimately this abbot was raised to the Bishopric of Crediton, which was the seat of the Devonshire Diocese about 910. In 1003 Exeter, after a gallant defence of some three months' duration, was betrayed by its governor into the hands of Sweyn. As has been said elsewhere, this king came from Denmark especially to punish Ethelred the Unready for having allowed the massacre of Danes, in which the sister of Sweyn had perished. The monastery of St. Peter was not spared, nor was the city, which did not recover from the terrible visitation till the accession of Canute.
From this time Exeter increased to such importance and wealth that in the reign of Edward the Confessor it was deemed advisable and for better security to make it the head of the Diocese.
For this purpose the Sees of Crediton and St. Germans (Cornwall) were united under one bishop. To uphold worthily the new dignity, the abbey church of St. Peter was erected into a cathedral by the Confessor, who appointed his chaplain Leofric as first bishop of the united see. Leofric had the monks removed to Westminster Abbey, and installed in their stead were twenty-four secular canons. The date of Leofric's installation is about 1040, which is, of course, that of the foundation of the Cathedral. This arrangement was altered on the re-erection of the Cornish See in 1876.