Original: The republican period of Ancient Rome began with the overthrow of the Monarchy c. 509 BC and lasted over 450 years until its subversion, through a series of civil wars, into the Principate form of government and the Imperial period.
Simplified: The republican period of Ancient Rome began with the overthrow of the Monarchy at about 509 BC and lasted over 450 years until its subversion, through a series of civil wars and the Imperial period.