It shows up in the opening credits, and may show up at least once an episode; I’m not sure that every episode has featured it. I’m not quite sure how to describe it other than as a big board with some sort of “pegs” that go into probably-not-randomly-spaced square frame things. I had thought that it might be some sort of calendar, but I’m not sure, and it’s never shown long enough for me to really inspect it.
I’m pretty sure it’s a calendar. They could take a whole episode to explain the Roman calendar, and Julius Caesar’s reforms to it. Viewership might really drop off, though.
I thought it was a large Calendar and notice set up in the Forum. I vaguely recalled references to such a thing elsewhere, but I can’t recall enough about it.
I like the way they start panning before where “July” and “August” would be, so you don’t see that August isn’t yet there (and when did they change it to “July”, anyway?)
The commentary in one of the early DVDs says that “they” don’t exactly know how it worked or what it communicated, although there are several theories. I don’t know if “they” meant the producers of the show, or historians.
I can get some vof them, I think. You’ve got the she-wolf that suckled Romulus and Remus. There’s also a pretty impressive Medusa, with flowing snales. An obscene grafitto of a soldier with a huge penis (with “arma” = “weapon” written next to it. A kinda pun.) There are geese and other animals. I’ve assumed the guy with the exploding head is a reference to Athena’s birth from Zeus’ head – but since the guy doesn’t look very Zeuslike, I assume it’s a reference to some leader who only thinks he’s Zeus.