Here's a site that gives you a lot more than at first appears - a kind of Tardis. From the page linked above you can choose any of 15 historical periods between the stone age and contemporary Greece.

Say we choose the obvious - the Classical Period. We then choose between Society, Economy, Politics and Culture. Let's go for Politics. We have 29 fairly short illustrated pages covering, first, the outline political history of the Classical period, and then the institutions of Athenian democracy, a page to each.

Links from key words to other pages, or, in the case of 'demagogue' for instance, to a pop-up definition, are frequent, and there are links to biographies of the leading men. Clicking on pictures brings a pop-up which not only enlarges the picture but also provides additional information.

I have not explored the whole site, but what I have looked at suggests that you could safely add it to the 'reading list' for essays on most Greek civilisation topics.

Thanks to Explorator for providing the URL. http://www.fhw.gr/chronos/en/