Dark Ages is a historically-based civilization-building game that features an innovative action selection mechanism. As long as your action markers remain on the board, you may be able to gain secondary bonus actions whenever you or another player repeat the action.

Dark Ages: Holy Roman Empire has the same core mechanisms as Dark Ages: Heritage of Charlemagne, but it focuses on Central Europe. As a result, it has a different game board. In addition, the card mixes are different, with different unique Culture Cards for the rulers, technologies and units. Furthermore, Heritage of Charlemagne contains a set of Vassals, which are missing from Holy Roman Empire. Instead, this version has a set of Relics.

The two sets also differ in micro-expansions ("modules") that are included. Holy Roman Empire contains the Crusades and The Pope modules.