The Tetrarchs, a porphyry sculpture sacked from a Byzantine palace in 1204 CE, Treasury of St. Marks, Venice

The Tetrarchy (Greek: "leadership of four"; aka the Latin Quadrumuirate, "government by four men") was a system of government created in 293 CE by the Roman Emperor Diocletian in order to solve serious military and economic problems in the Roman Empire. This involved dividing his power over the empire into east and west sectors: he retained control of the East and his colleague Maximian controlled the west. Eight years later, feeling more focus was needed on both civic and military problems, he furthered the division of power by naming one "Junior Emperor", or Caesar, under each "Senior Emperor", or Augustus. Thus the Tetrarchy, a rule of four, was established and lasted until c. 324 CE.

The Tetrarach sculpture is also known as The Four Emperors.

The first tetrarchs were

• Diocletian, Augustus of the East
• Galerius, Caesar of the East
• Maximian, Augustus of the West
• Constantius Chlorus, Caesar of the West.

Tetrarchies existed elsewhere in the ancient world: for instance, the kingdom of Galilee under Herod Antipas was a tetrarchy.