War with Parthian: Severus waged another brief, more successful war in the east against the Parthian Empire, sacking their capital Ctesiphon in 197 and expanding the eastern frontier to the Tigris.
Expansion in Arabian: He then enlarged and fortified the Limes Arabicus in Arabia Petraea.
Expansion in North Africa: In 202, he campaigned in Africa and Mauretania against the Garamantes, capturing their capital Garama and expanding the Limes Tripolitanus along the southern desert frontier of the empire.
Invasion of Scotland: Severus traveled to Britain in 208, strengthening Hadrian’s Wall and reoccupying the Antonine Wall. In 209 he invaded Caledonia (modern Scotland) with an army of 50,000 men but his ambitions were cut short when he fell fatally ill of an infectious disease in late 210.
Rise of Army’s Status: He spent many years making major changes in the structure of the imperial government. Since his power rested on military might rather than constitutional sanction, he gave the army a dominant role in his state. He won the soldiers’ support by increasing their pay and permitting them to marry.
Decline in Power of General: To prevent the rise of a powerful military rival, he reduced the number of legions under each general’s control.
Decline in power of Senate: At the same time Severus ignored the Senate, which declined rapidly in power, and he recruited his officials from the equestrian rather than the senatorial order.
Decline in Power of aristocracy: Many provincials and peasants received advancement, and the Italian aristocracy lost much of its former influence.