kengr

Sure! Not necessarily two, of course; "triumvirate literally means 'three men rule' and there are examples other than the Roman, common enough that English still keeps the word around. "Duumvirate" is a much rarer word. Go figure.

Of course, there's also the Roman Tetrarchy, when Diocletian chopped up the Empire into four bits, but pointless history wanking is enjoyed only in colleges and the SCA. Hey, wait a second...