222-235 AD Ancient Rome Severus Alexander Silver Denarius Ancient Grades AU/MS. Marcus Aurelius Severus Alexander, also known as Alexander Severus, was a Roman emperor, who reigned from 222 until 235. He was the last emperor from the Severan dynasty. He succeeded his slain cousin Elagabalus in 222. Alexander himself was eventually assassinated, and his death marked the beginning of the events of the Crisis of the Third Century, which included nearly fifty years of civil war, foreign invasion, and the collapse of the monetary economy.