Compare the Roman Republic and the Greek city-state. What is common, are there any differences?

Note that in Greece the polity was different in different policies. Athens and Sparta are not the same thing at all. If we take Athens, then the execution of positions in the state was paid, in Rome, the execution of positions included in the magistracy was not paid, for it was considered an honorary duty. And so basically the features are common – citizens’ selectivity, responsibility, turnover.