Why did Diocletian retire from power in 305 CE?

Diocletian retired from his position as Roman emperor on May 1, 305 CE, for several interconnected reasons:

• Health and Longevity: After reigning for 20 years, Diocletian had aged prematurely due to illness.1
• Systemic Succession: To avoid future rivalries and ensure a legitimate, regular transition of power, Diocletian devised a solution within his tetrarchy system. He intended for the two senior emperors (the Augusti) to abdicate simultaneously, allowing the two junior emperors (the Caesars) to ascend to the rank of Augustus and appoint new successors.2
• Delegation: Having established a framework for the empire, he decided of his own volition to entrust the administration of the state to younger men.1

While he successfully implemented this transition, his decision to reject natural heredity in favor of this planned succession created significant political risks, as the military and the population remained deeply attached to hereditary principles. Following his abdication, Diocletian retired to a palace he had constructed near Salonae on the Adriatic coast.21