After deposing and killing the incumbent emperor Didius Julianus, Severus fought his rival claimants, the Roman generals Pescennius Niger and Clodius Albinus.

Later that year Severus waged a short punitive campaign beyond the eastern frontier, annexing the Kingdom of Osroene as a new province.

Following the consolidation of his rule over the western provinces, 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.

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.

With his second wife, Julia Domna, Severus had two sons; the elder, Caracalla, was proclaimed Augustus, or co-emperor, in 198, and the younger, Geta, in 209.

His mother's ancestors had moved from Italy to North Africa; they belonged to the gens Fulvia, an Italian patrician family that originated in Tusculum.

At the recommendation of his relative Gaius Septimius Severus, the emperor Marcus Aurelius (r. 161–180) granted him entry into the senatorial ranks.

[15] Membership in the senatorial order was a prerequisite to attain positions within the cursus honorum and to gain entry into the Roman Senate.

The Antonine Plague had thinned the senatorial ranks and, with capable men now in short supply, Severus' career advanced more steadily than it otherwise might have.

[22] Following the end of this term, Septimius Severus returned to Rome, taking up office as tribune of the plebs, a senior legislative position, with the distinction of being the candidatus of the emperor.

[23] About 175, Septimius Severus, in his early thirties at the time, contracted his first marriage, to Paccia Marciana, a woman from Leptis Magna.

The Historia Augusta relates that he heard of a woman in Syria of whom it had been foretold that she would marry a king, and so Severus sought her as his wife.

Her father, Julius Bassianus, descended from the Arab Emesene dynasty and served as a high priest to the local cult of the sun god Elagabal.

[30] In 191, on the advice of Quintus Aemilius Laetus, prefect of the Praetorian Guard, emperor Commodus appointed Severus as governor of Pannonia Superior.

He executed Pertinax's murderers and dismissed the rest of the Praetorian Guard, filling its ranks with loyal troops from his own legions.

At the same time Severus felt it reasonable to offer Clodius Albinus, the powerful governor of Britannia, who had probably supported Didius against him, the rank of Caesar, which implied some claim to the succession.

Afterwards, Severus declared his son Caracalla as his successor, which caused Albinus to be hailed emperor by his troops and to invade Gaul.

On 19 February 197 at the Battle of Lugdunum, with an army of about 75,000 men, mostly composed of Pannonian, Moesian and Dacian legions and a large number of auxiliaries, Severus defeated and killed Clodius Albinus, securing his full control over the empire.

[44] Abgar IX, titular King of Osroene but essentially only the ruler of Edessa since the annexation of his kingdom as a Roman province,[45] handed over his children as hostages and assisted Severus' expedition by providing archers.

His legions sacked the Parthian royal city of Ctesiphon and he annexed the northern half of Mesopotamia to the empire;[49][50] Severus took the title Parthicus Maximus, following the example of Trajan.

[53][54] According to Cassius Dio,[55] however, after 197 Severus fell heavily under the influence of his Praetorian prefect, Gaius Fulvius Plautianus, who came to have almost total control of the imperial administration.

After the assassination of Gaius Fulvius Plautianus in the rest of his reign, he relied more on the advice of his clever and educated wife, Julia Domna, in the administration of the empire.

[57] Upon his arrival at Rome in 193, Severus discharged the Praetorian Guard,[36] which had murdered Pertinax and had then auctioned the Roman Empire to Didius Julianus.

[69] Some scholars think that Eusebius' description of Severus as a persecutor likely derives merely from the fact that numerous persecutions occurred during his reign, including those known in the Roman Martyrology as the martyrs of Madauros, Charalambos and Perpetua and Felicity in Roman-ruled Africa.

The legatus legionis or commander of Legio III Augusta, Quintus Anicius Faustus, had been fighting against the Garamantes along the Limes Tripolitanus for five years.

Supported and supplied by a strong naval force,[77] Severus then thrust north with his army across the wall into Caledonian territory.

Retracing the steps of Agricola of over a century before, Severus rebuilt and garrisoned many abandoned Roman forts along the east coast, such as Carpow.

The enemy purposely put sheep and cattle in front of the soldiers for them to seize, in order that they might be lured on still further until they were worn out; for in fact, the water caused great suffering to the Romans, and when they became scattered, they would be attacked.

[79]By 210 Severus' campaigning had made significant gains, despite Caledonian guerrilla tactics and purportedly heavy Roman casualties.

[80] The Caledonians sued for peace, which Severus granted on condition they relinquish control of the Central Lowlands (of what is now Scotland)[75][81] as evidenced by the extensive Severan-era fortifications there.