in the pre-christian era, the most advanced civilizations developed along rivers and by the sea. The most advanced civilization was the Greek (and, later, Hellenistic) one. The position of Italy, not far from Greece, made it natural for Greek settlers to colonize southern Italy. This, in turn, paved the way for the Greek influence on the rising power of Rome
Rome also happened to be established on the larger river of central Italy, the river Tevere.
What's more, Italy is a peninsula with a very wide access to the sea, which accelerated the development of the technology of ship building.
These three factors (closeness to Greece, closeness to the sea, presence of a river) played a major role in the growth of Roman power.
