After Gallienus was assassinated outside Milan in the summer of 268 in a plot led by high officers in his army, Claudius was proclaimed emperor and headed to Rome to establish his rule.

Gallienus (; c. 218 – 268 ) was Roman Emperor with his father Valerian from 253 to 260, and alone from 260 to 268.

Based on the testimony of John Malalas and the Epitome de Caesaribus that Gallienus was about 50 years old at the time of his death, it is generally considered he was born around 218, son of Valerian and Mariniana, a woman possibly of senatorial rank and possibly a daughter of Egnatius Victor Marinianus, and brother of Valerianus Minor.

When his father Valerian was proclaimed Emperor on 22 October 253, he asked the Senate to ratify Gallienus ' elevation to Caesar and Augustus, in order to share the power between two persons.

The reason probably was the vacuum left by the withdrawal of troops for supporting Gallienus in the campaign against Ingenuus.

It is also suggested that the invasion was finally checked by Gallienus near Verona and he directed the restoration of the province, probably in person.

One more consequence of the catastrophe at the battle of Edessa was that Gallienus lost control over the two provinces of Germania, Britain, Spain and a large part of Gaul, when another general, Postumus, had declared his own realm ( typically known today as the Gallic Empire ).

Gallienus returned in 263 or 265 and, as even Historia Augusta admits, was entirely successful, finally besieging Postumus in an unnamed Gallic city ; however, during the siege, he was severely wounded by an arrow and had to leave the field.

Then there was a standstill until the end of Gallienus reign.

In 268, at some time before or soon after the battle of Naissus, Gallienus ' authority was challenged by Aureolus, commander of the cavalry stationed in Mediolanum ( Milan ), who was supposed to keep an eye on Postumus.

Then Gallienus laid siege to the city, but he was murdered during the siege.

Cecropius, commander of the Dalmatians, spread the word that Aureolus was leaving the city, and Gallienus left his tent without his bodyguard, only to be struck down by Cecropius.

One version has Claudius selected as Emperor by the conspirators, another chosen by Gallienus on his death bed ; the Historia Augusta was concerned to substantiate the descent of the Constantinian dynasty from Claudius, and this may explain its accounts which do not involve Claudius in the murder.

Gallienus was the father of some useful reforms.

In 259 a so-called Gallic Empire was established when Postumus rebelled against Gallienus.

At the time, it was known as the Year of the Consulship of Valerianus and Gallienus ( or, less frequently, year 1007 Ab urbe condita ).

At the time, it was known as the Year of the Consulship of Valerianus and Gallienus ( or, less frequently, year 1010 Ab urbe condita ).

At the time, it was known as the Year of the Consulship of Valerianus and Gallienus ( or, less frequently, year 1008 Ab urbe condita ).

At the time, it was known as the Year of the Consulship of Gallienus and Taurus ( or, less frequently, year 1014 Ab urbe condita ).

At the time, it was known as the Year of the Consulship of Gallienus and Faustianus ( or, less frequently, year 1015 Ab urbe condita ).

Their raids throughout the three parts of Gaul were traumatic: Gregory of Tours ( died ca 594 ) mentions their destructive force at the time of Valerian and Gallienus ( 253 – 260 ), when the Alemanni assembled under their " king ", whom he calls Chrocus, who " by the advice, it is said, of his wicked mother, and overran the whole of the Gauls, and destroyed from their foundations all the temples which had been built in ancient times.

Then an Athenian militia, led by the historian Dexippus, pushed the invaders to the north where they were intercepted by the Roman army under Gallienus.

On their retreat through the northern Italy, they were intercepted by Gallienus ' army near present day Milan and defeated in the battle of Mediolanum.

In Cologne, Gallienus son, Saloninus, and his supervisor Silvanus were installed by Gallienus in 258.

This shows that, after suppressing the revolt of Macriani, Egypt had returned to Gallienus ' control ; however, in spring of 262, the city is reported to be rent by civil tumult, as a result of a new usurpation.

Arch of Gallienus in Rome, 262 – dedicated to, rather than built by, Gallienus.

Gallienus has not been dealt with well by ancient historians, partly due to the secession of Gaul and Palmyra and his inability to get them back.

In particular large numbers of votive coins deposited by worshippers have been recovered at the Mithraeum at Pons Sarravi ( Sarrebourg ) in Gallia Belgica, in a series that runs from Gallienus ( 253-68 ) to Theodosius I ( 379-395 ).

The Heruls are first mentioned by Roman writers in the reign of Gallienus ( 260-268 ), when they accompanied the Goths ravaging the coasts of the Black Sea ( today southern Ukraine ) and the Aegean.

* Battle of Mediolanum: A Germanic confederation, the Alamanni ( 300, 000 warriors ), who crossed the Alps are defeated by Roman legions under Gallienus near Mediolanum ( modern Milan ).

* Gallienus established himself at Mediolanum ( modern Milan ), he reorganizes the army supported by elite cavalry and dispatch troops to the Rhine frontier.

* Saloninus, son of Gallienus, is proclaimed Augustus by his troops.

They march from Asia to Europe but are defeated in Thrace by Gallienus ' general Aureolus, and both are killed.

In the early summer of 268, the Emperor Gallienus halted their advance into Italy, but then had to deal with the Goths.

When the Gothic campaign ended in Roman victory at the Battle of Naissus in September, Gallienus ' successor Claudius II Gothicus turned north to deal with the Alemanni, who were swarming over all Italy north of the Po River.

* The Military Orientation of the Roman Emperors Septimius Severus to Gallienus ( 146 – 268 C. E.

Long before Diocletian, Gallienus ( r. 253 – 68 ) had already chosen Milan as the seat of his headquarters.

Aurelian's achievements are ignored, the revolt of Carausius is backdated to the reign of Gallienus, and it is implied that the Tetrarchs engineered Aurelian's defeat of the Palmyrenes ; the period between Gallienus and Diocletian is effectively erased.

As Marcus Aurelius and his adopted brother Lucius Verus had done a hundred years before them, Gallienus and his father divided the Empire ; Valerian struck for the East to stem the Persian threat and Gallienus remained in Italy to repel the Germanic tribes on the Rhine and Danube.

While spending most of his time in the provinces of the Rhine area ( Germania Inferior, Germania Superior, Raetia, Noricum ), it is almost certain that, during 253 to 258, Gallienus visited the Danube area and Illyricum.

During his Danube sojourn ( Drinkwater suggests in 255 or 256 ) he proclaimed his elder son Valerian II Caesar and thus official heir to himself and Valerian I ; the boy probably now joined Gallienus on campaign and when Gallienus moved west to the Rhine provinces in 257 remained behind on the Danube as the personification of Imperial authority.

However, somewhere between 258 and 260 ( the exact date is unclear ), Gallienus had to face the first major revolt in his reign.

Ingenuus, governor of at least one of the Pannonias, took advantage of Valerian's distraction with the ongoing invasion of Shapur in the East and the preoccupation of Gallienus with his problems in the West and declared himself emperor.

In any case, Gallienus reacted with great speed.