This one is for the coin collectors, have any of you folks come across forgeries that were made before the fall of the Empire. I know that after the fall of the Empire , a lot of the smaller kingdoms made copies in the Roman style.
Of course, there are plenty of examples of ancient counterfeit currency.
In the ancient world, (generally speaking) currency (coinage) was valuable primarily because it contained a certain quantity of of precious metal that was considered intrinsically valuable.
Therefore, there were two general methods of counterfeiting in ancient times. The first and easiest is knowing as "clipping" or "shaving" - since the metal in the coins was intrinsically valuable, you could remove a small amount of the precious metal off a coin, use the coin at face value, and keep a small amount of bullion for yourself. There are countless examples of clipped ancient coins still around today, and you can see some in the above link.
The second general method is similar to modern counterfeiting techniques. Counterfeiters would duplicate the appearance of a genuine coin, but use cheap base metals instead, either by plating a core of cheap metal with a small amount of the precious metal, or by alloying the precious metal with cheaper metal. The Wikipedia page on counterfeit money shows an example of a counterfeit coin from the rule of Domitian, and Coinweek has an article on the subject with plenty of even older examples. That article notes: "Fourées are even older than coinage itself – plated base metal bars have been found that were made to imitate ingots of precious metal used as currency before the introduction of coins."