How many Roman Empires were there? It depends on the year. As early as 253 CE, the Emperor Valerian thought the empire was too large for him to rule well.
He divided it into western and eastern halves, and gave the western half to his son to rule. He kept the eastern half. When Valerian died in 260 CE, his son took over the entire empire. In 284 CE, a general named Diocletian became emperor. He also thought the empire was too large to be ruled by one person. He gave control of the western half to a trusted officer. When their rule collapsed, civil wars again divided Rome. But in 324 CE, Constantine the Great, the first Christian emperor, managed to reunite the whole empire. In 395 CE, almost 60 years after Constantine’s death, the Roman Empire split in two again. The Eastern Roman Empire was based in Constantinople, and the Western Roman Empire was based in Rome. This time the division was permanent.