Who loves ya, baby?
1) small agrarian republic largely based on a slave economy, with extremely high value placed on personal honor and public service as function of that personal honor
2) becomes a world-spanning empire, defeating its mortal enemy in the process
3) only to find itself essentially adrift as the world's (the known world, for the Romans) only remaining superpower
4) finds itself engaged in imperial overreach, its traditions long ossified into corruption, wealth inequality yawning, might turned inward without a great external enemy to unite its people, the normalization of public violence, etc