What were the similarities between the Roman republic and the Greek polis?

The similarities were as follows:

1) Both the republic and the polis of Ancient Greece were formed from the community;

2) Both of these state formations were based on communal democratic principles.

But there was also a fundamental ideological difference:

1) Ancient Greek city-states defended the idea of their own independence and put freedom at the forefront, while in the republic the main idea was to defend the greatness of Rome.