The major similiarites are:
- Both systems allowed for some amount of input from all or most of the male citizens of the society.
- Neither was a monarchy, which is what just about every other society was in those days.
So both of these types of government are pretty unique for their time and that's a very important similiarity.
The major difference is that the Greek democracy gave more power to more people than the Romans did. The Romans had a direct democracy that got to vote on a lot of laws and have a part in carrying out the laws. Roman laws were made much more by elected officials (Senate) and carried out by government officials like consuls and censors rather than by more ordinary people.
So both were very democratic for their times, but the Greek system was more of a direct democracy and the Roman system was more like our representative democracy.
The similarities of the two governments are:
1. Both people groups did not espouse any type of king. The Greeks had a famous king who was greatly loved, Codrus. When he died they realized that no one would be better. So, they did away with kings. The Romans did away with kings, because they could not stand the evil of Tarquinius. So, they both did not have kings, but for different reasons.
2. They still had magistrates that rule on behalf of the people. The Greeks had archons and the Romans had consuls.
3. Both groups had a sophisticated laws.
Here is one difference to get you started.
1. The Greeks had something called ostracism, and the Roman did not have this practice.