Most are scratch built from scrap beaded styrofoam or foamboard. There are a couple of buildings from the Game Craft middle eastern foamboard and MDF line that I modified a bit. There is one small temple to the right of the Capitoline Hill in the picture that is a resin model I bought - I forget the manufacturer.
The statuary are just plastic figures of various scales. The columns are dowl rods or plastic cake decorations.