Final answer:
The Founding Fathers were most inspired by the Roman Republic and Athenian democracy, which informed the United States' republican form of government and the principles of citizen participation rooted in the Constitution.
Step-by-step explanation:
The ancient governments that most inspired the Founding Fathers of the United States were the Roman Republic and the Athenian democracy. The Roman Republic influenced the Founding Fathers' adoption of a republican form of government, where citizens elect representatives to act on their behalf, as seen in the current United States republic structure. The Athenian democracy inspired the concepts of citizen participation in governance. Cleisthenes, an Athenian leader, played an instrumental role in founding democracy in Athens in the late sixth century BCE.
After the American Revolution, the revolutionaries turned to republicanism as their government form, reflecting the influence of these ancient governments. America's democratic tradition has its roots in Greece and Rome's practices, the Protestant Reformation, and Enlightenment philosophies. These ancient and historical influences helped shape the United States Constitution and the democratic republic it established.