His games comprise a deck of cards, and then perhaps a few supporting items like money counters or victory point cards. There are two characteristic things about the cards. Firstly, each card can serve several purposes. In Glory to Rome, it can be a plan for a particular building, raw material for a building, an action somehow related to building (starting a building, adding material, robbing your neighbours), or a member of staff who carries out an action. Secondly, one mode of a card will have some sort of ability on it that modifies the rules, or lets you do different things. In Glory to Rome, if you build the insula (a Roman tower block), you can have three more staff than usual; if you build the scriptorium, you can now complete any building using one card's worth of marble.

The basic idea is fairly simple (but not trivial, because of the multiple uses of a card). But there is enormous emergent complexity. My brain fires on all cylinders while playing it.

This looks like a reasonable explanation of the rules:

https://ultraboardgames.com/glory-to-rome/game-rules.php