Conversation so far:
Did Julius Caesar cause his own demise?
Julius Caesar's populist and authoritarian reforms angered the elites, who began to conspire against him.
What was Julius Caesar's last greatest acheivement before his death?
Julius Caesar's last greatest achievement was his reform of the calendar, creating the Julian calendar

Question: What was the reason for the reform
Self-contained rewrite: What was the reason for Julius Caesar's reform?