Millennia ago, all legal documents used a system like these. Documents were dated in years of the reigning monarch (because using any other system was disrespe

Millennia ago, all legal documents used a system like these. Documents were dated in years of the reigning monarch (because using any other system was disrespectful), but the year would always change on a given date in order to help keep things consistent. When Alexander's realm was split into four friend/foe kingdoms, they agreed between them to start a common dating system, that all documents would count from a common date. OT - It seems that they tried to remove any memory of Alexander - we have very few docs from Alexander's time; much, much less than expected - presumably, holding such a document was forbidden. On some records (such as the astronomical tables) the dates were falsified, probably so as to deny his reign. The decision to make a common date was likely related.