Political map of Europe & the Mediterranean 28 April 224 (Battle of Hormozdgan): Elagabalus reigned for just under 4 years, until 222, when the Praetorian Guard deposed him in favor of his 14-year-old cousin Severus Alexander. The accession of Alexander, with his mother Julia Mamaea as regent, ushered in a period of peace in the Roman Empire, but in neighboring Parthia trouble was brewing, as Ardashir I and his rebel Sasanians exploited the civil war between Artabanus IV and Vologases VI to annex Elymais and Characene. Determined to crush Ardashir, Artabanus marched south in 224, only to be defeated and killed at the Battle of Hormozdgan.