Have a look at Rome Fantasy Pack II which is the second in a series of high-quality, modular, environment art packs inspired by Rome.
It features tons of high-quality materials and decals to lay out an interior space, add vaulted ceilings with or without gilded decor, modify the color of the walls, then add colorizable fresco decals to give it an authentic look.
You can get more details and buy the pack here.