Barracks emperor

Aureus of Probus (r. 276–282), showing him in armour

A barracks emperor (also called a "soldier emperor") was a Roman emperor who seized power by virtue of his command of the army. Barracks emperors were especially common from 235 to 284 AD, during the Crisis of the Third Century, which began with the assassination of Severus Alexander. Beginning with Maximinus Thrax, there were approximately fourteen barracks emperors in 33 years, which produced an average reign of a little over two years apiece. The resulting instability in the imperial office and the nearly-constant state of civil war and insurrection threatened to destroy the Roman Empire from within and left it vulnerable to attack from external adversaries.