Geography determined the site which became Rome because there were important benefits to settling there.
The story starts with the Italian Peninsula as a whole. Running down its spine stretches the Apennine Mountains, which take up some three fourths of the total area of the peninsula. The area east of the mountain range, that bordering the Adriatic Sea, is pinched and narrow with little arable land. North and east winds make the eastern shore cool and drafty. Nature planned for Italy to look westward rather than eastward.
With a two thousand mile coastline, one would imagine Italy as a seafaring nation -- but no. There are very few natural harbors and those were taken by the Greeks for their Magna Graecia. With virtually no tidal activity, the Mediterranean cannot wash away the silt from the river deltas to help make them into adequate harbors.
South of the hills of Etruria, where the Tiber and Arno flow, there are two plains named Latium and Campania. The soil there is rich, fertile, and full of volcanic ash. Abundant streams provide irrigation and a gentle southwest wind blows across the plains. But for many centuries the plain of Latium was inhospitable to man. As late as 1000 B.C. there were active volcanoes in the region -- more than fifty craters within twenty five miles of Rome.
Fifteen miles from its mouth, the Tiber winds through a group of hills that rise from the plain of Latium. Far enough from the sea to be protected from piracy, the original Roman settlements occupied six of the famous seven hills of Rome. The heights commanded a view of the Tiber valley adjacent to the best ford on the river. The hills were wooded, precipitous and defensible even though the lowlands between them were marshy and subject to flooding from the river. Geography provided protection from enemies. Geography through the Tiber and its ford provided the opportunity for trade. Geography described a soil rich in nutrients -- the same soil that would build a great agrarian society.