Lineage or Legions? Explaining Imperial Rule Duration in the Roman Empire

Abstract One widely derided aspect of autocratic regimes is that they frequently feature nepotistic systems for political organization and management of power transfers, with inexperienced or unqualified individuals taking power solely because of their familial relation to the prior ruler. Such systems are thought to be more unstable and ineffective, reducing desirable outcomes for autocratic leaders, as well as the states they govern. We argue that this characterization ignores several important features of autocratic governance: rulers must constantly negotiate with other elites and rely on political networks based around loyalty and agreed-upon divisions of power, spoils, and prestige. Beneficiaries of nepotism enter office with many advantages that should make their reigns more stable and effective than those of less connected rulers. Specifically, we find evidence from the backgrounds and tenures of Roman emperors that dynastic relation to the previous ruler explains the likelihood of an emperor surviving in office without deposal as well as their effectiveness while in office. Rulers with close familial ties to their predecessor enjoyed longer rules and were associated with periods of imperial prosperity. Moreover, we also find that youth in autocratic office is a strong predictor of longevity without deposal, and that young rulers came to power owing to their dynastic relation to a predecessor.