Over a period of about 100 years, Roman moneyers issued so-called Nummi serrati from time to time. The edges of those coins were serrated – a rather laborious method of coinage. The edges of the coin blanks were cut before the coins were minted.
Nummi serrati were much more difficult to counterfeit than coins with normal edges. But whether this was really the reason for this method is unclear. It could also have been a way to prove the authenticity of the coins, or to guarantee their silver content. Or maybe it was just a fashion that some moneyers adopted and others did not.