Which ancient principles can be found in American government today?

The government of the United States borrows a number of important principles from ancient civilizations, namely classical Greece and Rome. While much of the structure of today's government is more of a direct outgrowth of the Enlightenment of the seventeenth century, many ancient ideas are present in it as well.
The eighteenth-century French philosopher Baron de Montesquieu gets a lot of credit for the idea of a government made up of separate branches with different powers. However, the idea goes much further back. The Greek philosopher Plato first promoted the idea in the fourth century BCE. He wrote in The Laws that a successful government should combine the functions of a democracy, an oligarchy, and a tyranny so that the people would benefit from the positives of each without being subjected to all their negative aspects. The idea of three separate branches with different powers similar to today's Executive, Legislative, and Judicial branches was later formulated by Aristotle, Plato's student. This idea of a mixed form of government would inspire later philosophers and the framers of the United States Constitution.
The form of our legislature also borrows many ideas from the Roman Republic. Rome was too large to have a direct democracy like Classical Athens. Instead, eligible citizens elected representatives to make laws on their behalf in the Senate. The legislature of the United States is likewise composed of elected representatives.