The reigns of Trajan, Hadrian, Antoninus Pius and Marcus Aurelius (collectively 98-180 ce) were for the most part years of peace and prosperity for the Roman empire. Partly this was because each of them was appointed on merit by his predecessor, with senatorial approval, rather than according to hereditary principles. Unfortunately, Marcus Aurelius chose to succeed him his unstable son, Commodus, on whose assassination (192) a civil war broke out. The victor, Septimius Severus (193-211), instituted a more militaristic, antisenatorial regime which outlasted his dynasty, though the temporary stability he had restored did not. Severus’ son Caracalla, Caracalla’s murderer Macrinus, Macrinus’ successor Elagabalus and Elagabalus’ successor Alexander Severus were all, one after another, assassinated or put to death (between 217 and 235).