Didascalicon, Book IV: the order and number of the divine books
Chapter XI. On the canons of the councils
Canon in Greek is interpreted in Latin rule. It is called rule because it leads rightly and never draws aside. Others said it is called a rule either because it rules, or because it affords the norm of living rightly, or because it corrects what is twisted and depraved. The canons of the general councils began from the times of Constantine. For in the preceding years, with persecution raging, there was no opportunity of teaching the people; hence Christianity was split into various heresies, because there was no license for the bishops to assemble together, except in the time of the aforesaid emperor. For he gave to Christians the power of assembling freely. Under him also the holy Fathers, assembling in the Council of Nicaea from the whole world, handed down, according to the evangelical and apostolic faith, the Creed second after the apostles’.