Old Metal

Gold and silver can be preserved in mint state even after 2,000 years. Especially gold.  Roman Republic denarii are affordable in very fine condition or worse, unless of an exceedingly rare type or associated with a famous person or event (Sulla, Pompey Magnus or Sextus, Caesar, Brutus, Cassius, Augustus, Agrippa, Marcus Antonius, etc.)  Before Augustus, most of these denarii can be traced to a single year date, based on the name or initials of the monetalis (moneyer) appearing somewhere on the coin.  So, you can line up denarii of the Roman Republic in order and say what we know from ancient sources about the events of that year.  Many other ancient coins, and even medieval coins, can only be traced to within a couple decades, based on the reign of a ruler.  Not until the 1500's do arabic numeral dates we can recognize ("1595") start appearing on coins.