This is where the Roman Forum was. It was effectively a public square where the citizens gathered to discuss the affairs of the state. Nearby are the temples where they worship their gods. Affairs of the state and religion are intertwined in those days. The Romans, inheriting from the Greeks, developed the republican government, or representative democracy - in which elected individuals represent the people in the government. And this is the center of it all.
The Romans built great buildings such as the Coliseum and the Pantheon. They built great roads such as the Appian Way. They built the aqueducts to supply the city with water. They made Latin the lingua franca. They made Christianity practically universal. But in my opinion, together with the Greeks, their greatest contribution to the world is the republican system of government. It may not be the perfect way to govern, but no one has come up with a better way yet.