I have always been impressed by the elegance, symmetry (and relative modesty) of the tetrarchy founded by Roman emperor Diocletian (245 - 316). Is it something that was invented at the time or does the system draw directly on earlier precedent?
I don't know of any other college of leadership without any ties of family anywhere else in Roman history or any other culture. It would seem to have been Diocletian's creation, fit to the conditions of the crisis of the time, so that the other three leaders would be too busy sustaining the empire to worry about anything else.
The virtually instant collapse of the system on Diocletian's retirement is a good indicator that it needed both Diocletian and the crisis to work. Once both were even slightly out of the picture it did nothing but encourage a series of civil wars.