The characteristics that both the Roman Empire and the Roman Republic shared include:
- They expanded Roman territory through conquest.
- They included the senate as a part of government.
- They took a census to reform the tax system.
The first option, "They invested all power in one supreme leader," is not applicable to the Roman Republic, as it was characterized by a system of checks and balances and shared power, while the Roman Empire did have a supreme leader in the form of the emperor.