The Ancient Roman Republic (when not being ruled by a dictator) had a group with similar structure to the United States Congress and had up to two Consuls which were elected by the people, similar to the United States President.
As Americans are, ancient Romans were afraid of your name and dictatorship reeking habit and there civilizations. So, they formed a republic that would keep power evenly distributed throughout the state. In the group similar to the United States Congress, a group would represent The common people of Rome and the wealthy people of Rome. This would represent the voices of all Roman citizens. The consuls, elected into consulship, served rolls very similar to the American president in terms of leadership, rolling, and military order and decisions. These similarities make the government systems of ancient Rome and The United States very comparable