While Septimius Severus was settling affairs in Rome after his successful coup of Didius Julianusí government (AD 193), the governor of Syria was still preparing his own bid for Roman supremacy. The source information on Gaius Pescennius Niger is relatively obscure, be he seems to have been an Italian of equestrian heritage and was born in approximately AD 135. After serving with some military acclaim in Dacia, he seems to have been made a suffex consul (late 180ís AD) and had been appointed to govern Syria as a trusted lieutenant of Commodus in AD 191.
Word of the assassination of Commodus on December 31 AD 192 likely traveled slowly into the further provinces of the empire. Pertinax was probably well established as a replacement by the time Niger was aware of his benefactors death, but the idea of usurpation, despite Pertinax also having been a supporter of Commodus, may have been established as soon as the news arrived. However, it wasnít until the murder of Pertinax and the short reign of Didius Julianus that revolt was openly set in motion. The people of Rome began to riot in clear opposition to Julianus as soon as he arrived in Rome following Pertinax murder on March 29, AD 193. The mob seized control of the Circus Maximus and called for the popular general Niger to return to Rome and claim the throne for himself, before dispersing peacefully the following day.
When word of reached Niger in Antioch, he understandably envisioned himself the peopleís champion and had himself proclaimed emperor by his readily supportive legions. Despite what can be assumed to be a cordial relationship between Niger and Severus (who were both ardent Commodian supporters), Niger immediately began to consolidate his control of the east while Severus made a deal with Clodius Albinus (another potential rival) in Britain (making him his heir in order to gain his support) thereby securing the west. While Severus marched on Rome, Niger moved from Antioch to Byzantium as a foreboding token of his proximity to the territories of Severus. He legitimized his own cause as the champion of the people and avenger of Pertinax by adopting the title ďJustusĒ (the just). Attempts to get messages to Rome in order to supersede any claims by Severus to the throne were intercepted and conflict was inevitable.
For Niger to make good on his own claim, he pressed the issue and moved against Severus. He did so by marching west into Thracia towards the coastal city of Perinthus. Despite numerical advantages he was repulsed by Severan loyalists and marched back to his stronghold at Byzantium. Niger attempted to offer an olive branch to Severus in the form of a joint rule compromise, but Severus rejected this flatly. Conversely, an offer by Severus to allow Niger to go into voluntary exile unmolested was equally snubbed. Meanwhile, Asellius Aemilianus the proconsular governor of Asia and a supporter of Niger moved an army against Severan forces near Cyzicus on the coast of the Propontis. Aemilianus himself was killed in the engagement but the two armies continued to jockey for position while moving east into Bithynia.
Near Nicea, Niger arrived to take personal command facing the Severan commander Candidus (despite Severus himself having moved into the region by this point in late AD 193). It was here that a decisive battle was fought in the narrow passes between Nicea and Cius, with the outcome in doubt throughout. Each side held the advantage at several junctures, but ultimately Candidus forced Niger to retreat under cover of darkness. Niger moved south into Syria, stopping at Antioch while Candidus consolidated the Severan position in the Asia region.
In the Spring of AD 194, a Severan army under the command of Valerianus and Anullinus marched south from Cilicia towards Nigerís position in Syria. At the ĎCilician Gatesí (a narrow pass through the mountains with high mountains on one side and cliffs above the sea on the other) Niger positioned his army on a well fortified hill and prepared for the assault. Initially the defenderís position proved superior but a severe thunderstorm erupted that had the effect of confusing and disrupting Nigerís forces (Dio Cassius implies divine intervention, but the effects of the storm certainly played a role in the mindset of both armies). By the end of the battle some 20,000 of Nigerís army had been killed and though Niger himself escaped he was soon captured and beheaded near the Euphrates.
With the result of the battles at Cyzicus, Nicea and the Cilician Gates, any remaining support for Niger and resistance to Severus in the east waned. Severus also earned a harsh reputation in dealing with Nigerís supporters, though few of the aristocracy were victimized to extremity beyond financial penalty and/or exile. Citizens of cities loyal to Severus were rewarded for their support while cities such as Antioch and Byzantium were stripped of various legal rights among other punishments in response to their support of Niger.
With his victory over Niger, Severus continued for a short time to assert his authority in the east and led punitive campaigns against the Osroeni, the Adiabeni, and the Arabians. As many of Nigerís remaining supporters fled to Romeís eastern rival Parthia, Severus planned additional attacks into Mesopotamia and beyond in order to assert his authority. Much like the conqueror emperor Trajan of a century before, Severus looked to expand the empireís borders and did so by annexing Mesopotamia as a province. However, Severusí continued eastern adventures would have to wait, as the defeat of Niger allowed an opportunity to confront another rival. Despite having already named Clodius Albinus his heir, Severus named his own son Caracalla as Caesar in a clear affront to the governor of Britain (though there is some contention that Albinus had been actively undermining Severus in the west during the war with Niger). As Albinus prepared his own army for war, Severus marched west with the intention of consolidating the entire Roman empire under his own power.