1 Marcus: What's that?
1 Julius: {holding a pot of something} Greek fire.
2 Julius: A sticky combustible compound that can be sprayed on enemies and can't be doused with water.
3 Marcus: Should you have a naked flame next to it?
3 Julius: Relax, it's perfectly safe.
4 [sound]: Fwackoom!

Greek fire was actually invented some time in the 7th century, and used by the successors of the Roman Empire, the Byzantine Empire, against their enemies. It was a sticky, highly inflammable fluid that was close to impossible to extinguish, somewhat similar to napalm. Its exact composition remains a secret lost to the mists of time. It probably wasn't highly explosive, but then again it's also a pretty sure bet that Romans like Marcus and Julius never saw it. If you're going to go for inaccuracy and anachronism, don't go halfway, I say.

This is only the second time the Romans have appeared on a different set to the generic "Roman columns" I usually use for them. I was getting a bit bored of those.