Soon after accepting the purple, the new emperor Trebonianus Gallus made a deal with the invading Goths. They were allowed to leave Roman territory with all their loot and prisoners and were even granted an annual tribute. It was a humiliating agreement, but what was worse was that, instead of pacifying them, it only emboldened the Goths. They would soon be back for more. Completely ignorant of this bleak future, Gallus travelled to Rome, where his co-emperor Hostilianus, a son of the late Decius, soon succumbed to the plague. The young man’s final resting place was likely the famous Grand Ludovisi Sarcophagus, which can nowadays be admired in the Museo Nazionale Romano.
Hostilianus was presumably a victim of the dreadful Plague of Cyprian, which by now had reached the centre of the Roman world. Those affected did not stand a chance. Now that one Augustus was dead, Gallus quickly promoted his own son Volusianus from Caesar to Augustus. The fourth century historian Aurelius Victor lauded father and son because “they meticulously and assiduously arranged the burials of all the poorest folk”. No doubt these people were victims of the plague as well.
The Persian menace
In late 252 or early 253, the Persian king Shapur I invaded Roman Syria. We do not know the exact year of the invasion, but since Zosimus discusses it as part of Gallus’ reign, late 252 or early 253 is a good guess. In the Res Gestae Divi Saporis, a trilingual inscription in the Persian heartland, Shapur claims that the casus belli was Armenia. That is all the information the inscription gives, but we may be able to reconstruct what had happened. The Persians had arranged for the murder of the Armenian king, Khosrov II, and had subsequently annexed the kingdom. Loyal Armenians had smuggled Khosrov’s infant son Tiridates out of the country and the boy had been given shelter in Rome. Shapur probably saw this as a breach of the treaty he had made with the emperor Philippus, a treaty that stipulated that Armenia was in the Persian sphere of influence.
The Res Gestae Divi Saporis make it clear that Shapur never intended to conquer and annex Roman territory. His aim was to punish the Romans by burning and pillaging as many cities and towns as possible. The Res Gestae claim the king destroyed a Roman army and temporarily captured 37 cities. The list of cities allows us to reconstruct his offensive with some degree of certainty. Shapur advanced along the river Euphrates and took Anatha, Dura Europos, Circesium, Sura and a number of forts before being checked by a Roman army at Barbalissus. We do now know anything about the composition of this army. Shapur claimed it was 60.000 men strong, but that sounds like a gross exaggeration, and we should not forget that the Res Gestae inscription is first of all a blatant piece of propaganda. Some of the Roman legions in the region likely participated in the Battle of Barbalissus, such as Legio IV Scythica, which was stationed at nearby Zeugma. We do know for certain that the emperor Gallus was not present at the battle. He had been in the East, as is attested by coins with the text ADVENTVS AVG (‘arrival of the emperor’), minted in Antiochia, but apparently he had left again by the time the Persians had reached Barbalissus.
We have no details of the Battle of Barbalissus. The battle is not even mentioned in Roman sources and Shapur merely stated that the Roman army was annihilated. After his victory, the king kept advancing along the Euphrates and captured several more cities, among them Zeugma. He subsequently took Germanicia (modern Kahramanmaraş in Turkey), named after the Roman prince Germanicus, and then swung south again towards Antiochia, the capital of the Roman province of Coele Syria. It seems that the city was betrayed to him, so there was no need for a protracted siege. Antiochia was thoroughly pillaged, many of its buildings were destroyed and large numbers of its citizens were led away in captivity. Among the captives were many Christians. Shapur then probably split his army into smaller columns, which moved east and south along the tributaries of the river Orontes and captured more cities and towns.
Among the settlements captured were Epiphania, which is modern Hama in Syria, and Raphaneae, the base of Legio III Gallica. At Emesa (modern Homs), the Persian column was finally checked by one Uranius Antoninus. In the Res Gestae Shapur also claims to have captured some cities in Cappadocia. This was probably a separate offensive, perhaps led by his son Hormizd. Even though the Persians left Roman territory again and the invasion ultimately amounted to no more than an exceptionally large raid, it was deeply humiliating for the Romans. They had suffered a sharp defeat and the most important city in the region had been sacked and depopulated. The emperor Gallus probably never realised the scale of the disaster. He and his son were soon dead.
Aemilianus and Valerianus
After leaving the Danube region, Gallus had appointed Marcus Aemilius Aemilianus as the new legate of Moesia Inferior. He soon observed that the Goths ignored the treaty they had made with Gallus. They may have interpreted the Roman concessions as a sign of weakness and quickly returned to resume their raids. But in 253 Aemilianus managed to surprise and rout them, and subsequently led a counter raid into Gothic territory. Many captives previously carried off by the Goths were freed. Since these were the days of the barracks emperors, the victorious Aemilianus was almost immediately proclaimed emperor by the troops under his command. The new emperor had been born on the island of Meninx (Djerba off the coast of Tunisia) and is described in the sources as a Moor or a Libyan. He was in his late forties and happily accepted the purple that was offered to him.
As Aemilianus and his forces marched to Italy, probably in July, Gallus and Volusianus mobilised their own forces. They also sent orders to Publius Licinius Valerianus, a general stationed in Rhaetia, to come to their aid with the Rhine legions from the Germanic provinces. Valerianus would not arrive in time. Aemilianus’ forces met those of Gallus and Volusianus at Interamna (modern Terni in Umbria), but there would be no formal battle. Gallus’ troops simply weighed their options and ultimately decided not to fight for him. Believing they might receive greater rewards from Aemilianus, they quickly murdered father and son and defected. Aemilianus did not enjoy his victory for long: he would be emperor for less than three months. After the murder of Gallus and his son, the Rhine army headed for Italy proclaimed Valerianus, a scion of an old senatorial family, the new emperor. History then repeated itself: Aemilianus’ soldiers had no taste to fight for him and killed their emperor near Spoletium. Valerianus was now sole emperor.
As one of his first acts, the new Augustus appointed his son Gallienus co-emperor. This was a smart move, as the emperor had to be everywhere at the same time. The Crisis of the Third Century was becoming ever more intense. Germanic tribes, including the Franks, the Alemanni and the Goths, were threatening the Rhine and Danube borders. The Persian invasion of 253 had been a great success and Shapur was widely expected to return. Nomadic tribes were threatening Arabia Petraea, Egypt and Numidia. In response to the latter threat, the new emperors decided to resurrect the old Legio III Augusta, which had been disbanded in 238. Gallienus would take charge of the western provinces, while Valerianus would travel east and prepare for a counteroffensive against the Persians.
- Aurelius Victor, De Caesaribus 30-32 (translated and annotated by H.W. Bird);
- Epitome de Caesaribus 30;
- Res Gestae Divi Saporis;
- Zosimus, Historia Nova, Book 1.24-29.
 De Caesaribus 30 (translation: H.W. Bird).