Sarolta A. Takacs, Isis and Sarapis in the Roman World (E.J. Brill: New York, 1995), p. 114-116.

      After Commodus' murder, the city prefect P. Helvius Pertinax, the choice of the Praetorian Guard, ruled for three months. His ractionary rule, an effort to reintroduce Aurelian principles of government and strict discipline, estranged the Senate and the powerful Praetorian Guard who quickly eliminated him.
      The Praetorians chose M. Didius Julianus to succeed Pertinax. The provincial armies reacted immediately. The legions of Pannonia superior proclaimed L. Spetimius Severus emperor at Carnuntum. ¹⁸¹ In Syria, another key province, the troops opted for C. Pescennius Niger. Septimius Severus, able to outmaneuver Pescennius, entered Rome on June 9. 193, one week after Didius' murder by the Praetorians, who had made him emperor two months earlier.
      In order to take care of Pescennius, Septimius Severus named D. Clodius Albinus, who had had a successful military career in Dacia and Germany, Caesar. Septimius defeated Pescennius, who had tried to secure his position from Byzantium. Caught near Issus, Pescennius was executed. Hearing of Pescennius' death, the legions in Britain proclaimed Clodius Albinus Augustus in 196. On the way to secure the German legions for himself, Clodius was defeated and killed near Lugdunum in 197. After four years of civil war, Septimius Severus emerged victorious. At this point, especially in view of the twelve years of Commodus' autocracy, the empire was ripe for modifications to meet the social, economic, and political problems of the day.
      In provincial matters it was important to secure the area east of Syria. Septimius Severus did this by creating a buffer zone between Parthia and Syria, whose legions had shown themselves once more an important factor and power broker in one man's struggle for the Principate. Osroene, located in north-west Mesopotamia and enclosed by the Khabur, the Euphrates, and on the north side by Mt. Masius,¹⁸² formed, together with the area of Upper Mesopotamia,¹⁸³ the province Mesopotamia, the wedge between the ever problematic Parthia and Roman Syria. Septimius Severus spent two years in the region. This was to ensure the functioning of the buffer zone and to bind the legions of the area to himself and his successors. Septimius Severus also realized that the economically important Egypt needed reorganization but was unaware that an increase of local control could not remedy the situation. A continuous siphoning of revenues and capital without an appropriate mechanism for maintaining the Egyptian production base had depleted the country since Augustus' time.
      The author of Septimius Severus vita in the HA (Historia Augusti), Aelius Spartianus, remarked that the emperor "enjoyed his trip to Alexandria all the more because of the religion of Sarapis."¹⁸⁴ Neither Aelius, nor any other author, provides more detail. Hence we can merely assume that Septimius Severus' visit to the Alexandrian Sarapeum happened in the context of paying homage to the god of the Ptolemies, the protector of Alexandria and the conservator imperii.
      The most intriguing evidence, however, is the protraits of Septimius Severus patterned on artistic depictions of Sarapis.¹⁸⁵ McCann has shown that portrait types of Antoninus Pius and Marcus Aurelius formed the basis for this artistic representation of Septimius Severus. On the Arch of Severus at Lepcis Magna is the image of the seated Severus, patterned presumedly on the cult statue of Sarapis in the Alexandrian Sarapeum, "in the midst of the Capitoline Triad with the eagle of Jupiter at his feet." According to McCann, the image portrays Septimius Severus' "adopted Roman heritage and his African background through the single, powerful image of the syncretistic Jupiter-Serapis."¹⁸⁶ Besides the fact that Septimius Severus did not have to 'adopt' Roman heritage and probably never felt African, the representation is part of a natural development which began with Vespasian's 'political' employment of Sarapis. Embedded in a specific ideological context, it had now found an artistic expression.
      It is interesting to note that there are no known coin issues with a Septimius-Sarapis combination.¹⁸⁷ Septimius Severus doubtless propagated the image of himself as a cosmocrator and might have thought himself divine or qualified for deification. This he could do as a divi filius in the context of a political and ideological system that had developed since Augustus created it.¹⁸⁸
      Three denarii with a depiction of the ambitious and learned, h filosofoV, wife of Septimius Severus, Julia Domna, on the obverse and Isis walking with Horus on the reverse, with the legend saeculi felicitas,¹⁸⁹ illustrate the dynastic aspiration of the family while employing the most suitable myth of imperial succession. Rome's new imperial dynasty promised political stability and economic prosperity.

181 T.D. Barnes, "The Family and Career of Septimius Severus," Historia 16 (1967), 87-107 and A. Birley Septimius Severus (London, 1971).

182 A. Von Gutschmid Geschichte Irans und seiner Nachbarlander von Alexander dem Grossen bis zum Untergang der Arsaciden (Tubingen, 1888)

183 A.H.M. Jones Cities of the Eastern Roman Provinces (Oxford, 1937), 216-26, Chapter 9: "Mesopotamia," and L. Dilleman Haute Mesopotamie et pays adjacents (Paris, 1962).

184 Sev. 17.

185 A.M. McCann The Portraits of Septimius Severus, Memoirs of the American Academy in Rome, vol. 30 (Rome, 1968).

186 McCann (1968), 53.

187 An association of Jupiter-Sarapis, on the other hand, exists. McCann (1968), 54 on a "reverse type showing Jupiter with the modius of Serapis on his head (...)."

188 McCann (1968), 209: "Both the Jupiter and Serapis allusions indicate Severus' claim to deification, a claim which was not new to Roman imperial art but had never before been so comprehensively and boldly stated. This strengthened claim to divinity associated Severus with the Savior-King images of succeeding emperors. Jupiter, the ruler of the upper world, and Serapis, the gods of the lower world, as well as Severus' historical allusions, are fused in the image of the emperor as a cosmocator which appears on his coinage. The earthly realm, the heavenly spheres, and the lower world are united in the one image of an all powerful ruler."

189 RIC vol. 4.1, nos. 577, 645, and 865.