The Roman Republic political and legal system have influenced modern day democracies. The two main elements we see in democracies today are a constitution, and checks and balances. In modern day government constitutions are used to define the government and specify what kind of powers the government can display. The Roman Republic had their own constitution. It also can explain the freedoms individuals have. The other element is checks and balances. Checks and balances are used to control the leadership of a democracy. Indiviuals who want to be the solitary leader must be checked and surpressed if they are suspected of becoming too powerful. An example would be Caesar. He tried to gain all the power, and was assassinated because of it. Modern democracies wouldn't take it to that extreme, but the individual would be stripped of there power.
Citation: "Roman Republic" 2010. Wikimedia Foundation, Inc. March 7 2010. http://en.wikipedia.org/wiki/Roman_Republic