Found this in Wikipedia
Plutarch, in like manner, tells of the early religion of the Romans, that it was imageless and spiritual. He says Numa “forbade the Romans to represent the deity in the form either of man or of beast. Nor was there among them formerly any image or statue of the Divine Being; during the first one hundred and seventy years they built temples, indeed, and other sacred domes, but placed in them no figure of any kind; persuaded that it is impious to represent things Divine by what is perishable, and that we can have no conception of God but by the understanding.”
Wow, I've never heard this before. I always was taught that the Romans were pagans. It seems like this religion went from monotheism to paganism.