From Phyllis Hartnoll’s “The Theatre: A Concise History”… This first quote is about the end of the Roman theatre, and how itinerant performers carried the traditions forward into the Christian era.

Meanwhile, the humbler entertainers of the classical world wandered across Europe, alone or in small groups. Among them were acrobats, dancers, mimics, animal-trainers with bears or monkeys, jugglers, wrestlers, ballad-singers, story-tellers. Carrying with them the germ of the theatre, ready to take root again when conditions proved favorable, they lived as best they could and handed on the skills and technical tricks bequeathed to them by earlier generations of mime-players.

There was also a short quote somewhere I can’t find at the moment about the root of theatre being in the “mimetic instinct of man” or something like that. I like this one about the commedia dell’arte as well, and the adoption of stock characters in medieval drama:

The practice of improvisation was no doubt helped by another outstanding peculiarity of the commedia dell’arte. The company was made up of actors who always played the same part. This was not type-casting as we know it today, but the lifelong assumption of a disguise with which the actor became so identified that he often lost his own personality in the process, or rather, so merged his own personality in that of the type he played as to create a distinct personage. In many cases the actor abandoned his own name for that of the character, and so made it even more completely his own.