Septimius Severus

Septimius Severus disbanded the existing Praetorian Guard, which had assassinated his predecessor Pertinax, and replaced it with loyal soldiers from his own Danubian legions. This reform militarized the guard and increased imperial control.

Septimius Severus, proclaimed emperor by his troops in Pannonia, marched on Rome and secured recognition from the Senate. He defeated rivals Didius Julianus, Pescennius Niger, and Clodius Albinus, establishing the Severan dynasty that ruled until 235.

Septimius Severus besieged and captured Byzantium after a three-year siege, as the city had supported his rival Pescennius Niger. Severus destroyed the city's walls and reduced its status, but later rebuilt it, foreshadowing its future importance.

Septimius Severus defeated his rival Clodius Albinus at Lugdunum (modern Lyon) in a massive battle. This victory secured Severus's control over the entire Roman Empire and eliminated the last major challenger to his rule.

Septimius Severus led a major campaign into Caledonia (Scotland) to subdue rebellious tribes. He repaired and strengthened Hadrian's Wall, and died at York in 211. The campaign achieved limited success and was costly in lives.