The Twelve Tables were the official rules o f the Roman Republic. They greatly benefited the plebeians (lower class, 95%), because the lawmakers and judges could no longer change the laws to suite their benefit. The Plebeians could also see what laws they have to obey when they were carved in stone and placed in public, so they could defend themselves if they were falsely accused.
The American Democracy and the Roman Republic
The American Democracy is probably based off of at least a few factors of the Roman Republic, as shown by the fact that both governments use a checks-and-balances system, both are divided into three different branches (Legislative, Executive, Judicial vs. Consuls, Senate, Assembly), both include a Senate as/in one branch, and at least one branch holds the power to veto. On the other hand, whereas Roman governmental positions were based on wealth, our governmental positions aren't affected by wealth or social status whatsoever.
The Hierarchy of Rome
If I was in the Roman Republic, I would want to be a Consul so I could veto any new laws I didn't like, and I would have the chance to rule completely for up to six months if necessary.
The Switch
Rome switched from a Monarchy to a Republic because the monarch was starting to gain too much power, so the people replaced the system with a form of government where power was spread equally through three different branches. The power each section held was made equal through the checks-and-balances system, where most laws (major laws, usually) were passed through all of the branches, so the law was given the "all clear" or vetoed before being released.
Patricians and Plebians
Patricians were the Roman upper class that made up about 5% of the population. The patricians were in control of the Roman land, government, and society. The plebeians were the Roman lower class who made up the other 95% of the population, and consisted of the Roman workers, farmers, merchants, etc.