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 in the period from 235 through 284, during the Crisis of the Third Century that began with the assassination of Severus Alexander. Beginning with Maximinus Thrax, there were approximately fourteen barracks emperors in 33 years, producing an average reign of a little over two years apiece. The resulting instability in the imperial office and the near constant state of civil war and insurrection threatened to destroy the Roman Empire from within and left it vulnerable to attack from external adversaries.