The city of Rome was the center of a vast territorial empire for over five centuries. Rome was first settled, like most other primary urban sites in Italy, in the late Bronze Age, at the end of the second millennium BCE, and it developed into a city-state during the first few centuries of the following millennium. In the late third and especially in the second century BCE, the expansion of Rome increasingly pushed up against other competing territorial empires. During the fourth and third centuries BCE, the Roman Empire extended rapidly in peninsular Italy by means of a vast number of separate one-to-one treaties with the other cities, without the creation of an explicit confederation or of a clear imperial political infrastructure. Once the Mediterranean urban world had been almost completely unified under Rome, it collectively turned its renewed attention to the vast continental expanses of western and central Europe and of western Asia.