It is from Roman law that we inherit our system of democracy and the idea of the middle class.  The Romans were the first to institute direct election, though they did not have an electoral college.  The concept of a middle class orginates with Roman and Greek law.  There emerged an electorate that was not slave class nor was it aristocracy.  This class consisted of land owners of no noble blood.  Western tradition is dependent on both democracy and its components as well as the strength of the middle class.  Plato and Roman law were the first to address the characteristics of both democracy and the middle class. As this question is linked to Plato's Republic,  it should be emphasized that Plato was not a proponent of democracy and considered it a transitional form of government.  He pointed out that the majority was not always correct in its desires and attitudes and that allowing the majority to rule could potentially have dire consequences. 

Roman law became the foundation on which all legal concepts and systems were based, and its influence can be traced to this day in all Western legal systems. The study of canon law, the legal system of the Catholic Church, fused with that of Roman law to form the basis of the refounding of Western legal scholarship. The ideas of civil rights, equality before the law, procedural justice, and democracy as the ideal form of society, and were principles which formed the basis of modern Western culture. These ideals tie into the form of most Western governments, republics which use elected officials to speak on behalf of the people. The Romans used their Senate (sound familiar?) to carry out this job. In such a government, the system can only succeed if the people agree to uphold a standard of behavior. Should every citizen seek corruption as a means to an end, the systems fails.

Plato knew this in his day. The Republic is a brilliantly scripted piece of writing in which a conversation amongst intelligent peers leads the conclusion that people must be treated fairly and people must uphold a code of conduct. Look at our system of law today, and at the judicial system. The ideas of the Greeks and Romans are still usable today.