Constantine furthered the decline of the city of Rome primarily by moving the imperial capital from Rome to Byzantium, which he renamed Constantinople in 330 AD. This shift redirected political, military, and economic focus away from Rome to the new eastern capital, diminishing Rome's importance within the empire

. Additional factors include:

• Constantine disbanded the Praetorian Guard, an elite military unit traditionally based in Rome, which reduced the city's military significance and influence

• His religious policies favored Christianity and led to the decline of traditional Roman pagan cults and values, altering Rome's cultural and religious landscape

• The relocation of the capital to Constantinople, strategically positioned at the crossroads of Europe and Asia, made the eastern part of the empire the new hub for trade, culture, and military strength, accelerating the East-West divide that contributed to the Western Roman Empire's eventual fragmentation

While Constantine stabilized and reformed the empire in many ways, these decisions collectively weakened Rome's central role and prestige, setting the stage for its decline in the centuries that followed.