At the beginning of the year, a large Roman army was camped near Edessa in Mesopotamia for a new invasion of the Parthian Empire. The Parthians themselves had not sat still. Artabanus had gathered his forces, and so a violent confrontation seemed imminent. It was not to be so.
Before launching his new campaign, Caracalla wished to visit the temple of Sin – a moon god known to the Romans as Lunus or Luna; the gender of this deity is not entirely clear – near Carrhae. Carrhae had been the location of Crassus’ disastrous defeat at the hands of the Parthians in 53 BCE, but now the city was under Roman control and had been given the status of a Roman colony. The emperor left Edessa with just a small escort of horsemen. Among them was one Julius Martialis. Cassius Dio writes that he was an evocatus who held a grudge against Caracalla because the latter had refused to give him the rank of centurion. Herodianus claims he was in fact a centurion with the praetorians who had been bullied by the emperor, who had called him a coward and a country bumpkin. More importantly, the emperor had been responsible for the execution of his brother.
On 8 April, on his way to Carrhae, Caracalla stopped his horse to answer the call of nature. Martialis approached the emperor, grabbed the dagger that he had concealed underneath his clothes and stabbed Caracalla to death. After his deed, Martialis tried to get away, but he was chased and killed by the emperor’s loyal Germanic bodyguards (Dio claims he was killed by a Scythian, “for the emperor kept Scythians and Germans about him”). All the soldiers in the emperor’s escort assumed that this was the action of a lone wolf, who had held a personal grudge against Caracalla. The praetorian prefect Marcus Opellius Macrinus ordered the emperor’s body to be cremated and sent the ashes back to Julia Domna in Antiochia. Hearing of her son’s death, Julia committed suicide. The urn containing Caracalla’s ashes was brought back to Rome by the other praetorian prefect, Adventus, where it was placed in Hadrian’s mausoleum. Julia’s urn was first placed in the tomb of Gaius and Lucius, perhaps part of Augustus’ mausoleum, and then transferred to Hadrian’s tomb by her sister Maesa. Geta also presumably found his final resting place there, although there is a rival tradition that he was buried in his own tomb on the Via Appia.
A Moor on the throne
Macrinus had been there when Caracalla was murdered and he had cried his eyes out at the scene. But he was not as innocent as he tried to look. It was he, in fact, who had orchestrated the whole affair. Macrinus had persuaded Martialis to stab the emperor to death, so he was very pleased that Martialis had been killed as well and was no longer able to reveal anything about the conspiracy. Since the soldiers considered Adventus to be far too old for the throne, they chose Macrinus as the next emperor. He was given the imperial robes on 11 April, on the birthday of Septimius Severus.
Back in Rome, the Senate was quite pleased with Caracalla’s death, so it had no problems with accepting Macrinus as emperor. Macrinus was a Moor (Μαῦρος) from Caesarea in Mauretania (now the city of Cherchell in Algeria). He was an excellent lawyer, but not a very experienced soldier. Through his friendship with the late Plautianus and – later – Caracalla he had obtained high positions. Caracalla had given him assignments as a procurator and had subsequently made him a praetorian prefect. Macrinus would become the first emperor who was merely a knight (eques), and who was not from the senatorial class, as was traditional. He did adhere to other traditions though: in accordance with Moorish customs, one of his ear lobes had been pierced so that he could wear an earring. It is hard to say what disgusted the historian Cassius Dio more: his low birth, or this feature.
It seems the new emperor spent the remainder of the year undoing some of Caracalla’s measures. Dio writes that he abolished Caracalla’s ten percent tax on the emancipation of slaves and on inheritances. He also rewarded Adventus by designating him consul for the next year, making him a senator and giving him the office of praefectus urbi. The Historia Augusta claims that Macrinus was also responsible for the deification of his predecessor Caracalla. He may have done this to please the soldiers and to cover up his own crime.
Towards the end of the year, with winter approaching, the Parthian king Artabanus invaded Mesopatamia. He had not forgotten what had happened the previous year and was eager for revenge. Artabanus had gathered a large force of archers, cavalry and camel riders. Macrinus was not a soldier, nor a very good commander, and he tried to make peace with him, laying the blame for the war on Caracalla. But Artabanus demanded that the Romans abandon Mesopatamia and pay a large indemnity. This was not acceptable and both forces met near Nisibis. We have two versions of the battle that ensued. Dio’s version is short and fragmentary. He claims the battle began as a fight between soldiers over a water well. The Romans suffered a defeat and nearly lost their camp. They were saved when the Parthians mistook a group of camp followers for a second Roman army.
Herodianus tells a completely different story. The Roman and Parthian army fought each other for three consecutive days. From his account:
“The Romans had arranged their divisions carefully to insure a stable front; the cavalry and the Moroccan [i.e. Moorish, like Macrinus] javelin men were stationed on the wings, and the open spaces were filled with light-armed and mobile troops that could move rapidly from one place to another. And so the Romans received the charge of the Parthians and joined battle. The barbarians inflicted many wounds upon the Romans from above, and did considerable damage by the showers of arrows and the long spears of the mail-clad [cataphract] camel riders. But when the fighting came to close quarters, the Romans easily defeated the barbarians; for when the swarms of Parthian cavalry and hordes of camel riders were mauling them, the Romans pretended to retreat and then they threw down caltrops and other keen-pointed iron devices. Covered by the sand, these were invisible to the horsemen and the camel riders and were fatal to the animals. The horses, and particularly the tender-footed camels, stepped on these devices and, falling, threw their riders.”
Both sides suffered heavy losses. The Romans could not defeat the Parthians, and the Parthians could not defeat the Romans. In the end, negotiations were opened and a truce was concluded. Constant diplomacy would lead to a peace agreement the next year.
– Adrian Goldsworthy, The Fall of the West, p. 74-78.