Diocletian's tetrarchy established a four-rule system. How many rulers were part of this arrangement?

• A. Two
• B. Three
• C. Five
• D. Four

Answer: (D)

The arrangement is built around the idea of four rulers sharing imperial power, a deliberate system to stabilize succession and manage a sprawling empire. The term tetrarchy combines Greek for four with archy, so it literally means rule by four. In practice, Diocletian and Maximian served as the senior rulers (Augusti), while Galerius and Constantius I acted as junior rulers (Caesares). This setup distributed authority across East and West and created a built-in mechanism for succession. Therefore, the number of rulers is four. This fits the name and the intended governance. Other counts describe different models—a two-person rule would be a diarchy, three would be a triarchy—while the tetrarchy explicitly denotes four.