Several of the business transactions that take place throughout the film are done so exchanging Roman drachmas for various goods. The drachma was a form of currency used by the Greeks, never the Romans.
When the fly is buzzing around in front of the Roman guard's face (just before he eats it), if you look carefully, as it flies in front of his face, you can barely see the string holding up the fake fly being dangled in front of the actor's face.