Do you know what you're asking? It's a whole book! Look it up to wikipedia, there are different periods of governmental systems in Rom and Greece. Bear in mind that: 1. Greek civilization is prior to Roman. 2. Greece wasn't united in ancient times, it was divided into many small states and they had different political systems, you probably mean DEMOCRATIC ATHENS. 3. Romans had also three different political systems, you probably again mean republica romana, isn't it?