Factual error: There's a blackboard in one of the scenes when there's about to be a gladiatorial contest. The Romans may have had blackboards then, but the writing on it is wrong. The sort shown takes time to chip into stone used on statues, etc, and I suppose it would take quite a long time just to write things on a blackboard. The Romans had different writing for things like that, as shown in the graffiti in Pompeii. It's more flowing, and I expect it's quicker to produce.