When did fellatio start?

It all began in the 12th century A.D. when Sir Romulus III was walking to his weekly game of badmitten. On this particular day, Sir Romulus opted to take a shortcut through the Pennywinkle Forest. Hiding beneath a patch of bush beside the path, a derelict lay performing a handjob on himself (which was known as "priming the Pope" in those days. Well, Sir Romulus was not minding the path when he tripped over a root growing in its midst. He tried to keep his balance but could not and he fell face first into the bushes. As you might imagine, his mouth came down right upon the derelict's erect wanker (which is why it is referred as "going down" on someone) and, as the derelict was on the verge of ejaculation, he blew his wad of creme brule right down the throat and into the gullet of Sir Romulus III. Then, in order to ammend the situation, the both of them agreed that it was only propper for the derelict to suck off Sir Romulus, thus squaring the debt and that is why to this day ettiquette tells us that "we musn't get it, lest we are willing to give it". And that, my comrades, is the history of the first fellatio.