(τετράρχης/tetrárchēs, τετραρχία/tetrarchía).
I. Definition
The noun tetrarches (from τετράς/tetrás = 'entity of four parts' and ἄρχειν/árchein = 'rule') designates a military rank, but specifically the head of a tribal area within a fourfold alliance (tetrás or tetrarchía); subsequently a ruler of lesser rank (see below III.). The two meanings were brought together at the time of Diocletian, so that th…