Germanic tribes had crossed the Rhine and…

Maximinus spends most of his reign fighting invading tribes along the Danube and the Rhine.

The numerous milestones displaying his name attest to his energetic reconstructions of the roads in these regions.

The Roman Empire is plagued by internal strife and economic crisis  in the third century CE. Two ethnic Illyrian emperors, both born in Southeastern Europe, take decisive steps to prolong the empire’s survival.

• Emperor Diocletian, born in Dalmatia, implements strong central control, establishes a bureaucratic system, and abolishes the last remnants of Roman republican institutions. In an effort to strengthen loyalty to the state, he launches a persecution of Christians, seeking to reduce their allegiance to the church.
• Emperor Constantine, born near Naissus (modern Niš, Serbia), reunites the empire after years of turmoil, introduces dynastic succession, and in 330 CE, founds a new capital at Byzantium, later named Constantinople. He also legalizes Christianity, marking a pivotal shift in Roman religious policy.

The Augustan History (Latin: Historia Augusta), a late Roman collection of biographies, in Latin, of the Roman Emperors, their junior colleagues and usurpers of the period 117 to 284, presents itself as an assemblage of works by six different authors (collectively known as the Scriptores Historiae Augustae), written in the reigns of Diocletian and Constantine I, but the true authorship of the work, its actual date, and its purpose (if any), have long been matters for controversy.

Despite major problems, themselves of considerable interest, with the nature of the sources it used, and how much of the content is sheer fiction, it is the only continuous account for much of its period and is thus continually being reevaluated, modern historians being understandably unwilling to abandon it as a unique source of possible information, despite its obvious untrustworthiness on many levels.

The youth and good nature of the late Gordian III, along with the deaths of his grandfather and uncle and his own tragic fate, possibly at the hands of another usurper, grant him the everlasting esteem of the Romans.

Despite the opposition of the new emperor, the Senate deifies Gordian in order to appease the population and avoid riots.

Philip, unwilling to repeat the mistakes of previous claimants, and aware that he has to return to Rome in order to secure his position with the senate, leaves his brother Gaius Julius Priscus, who had been a member of the Praetorian guard under Gordian III, as extraordinary ruler of the Eastern provinces.

In Rome, Philip is confirmed Augustus, and nominates his young son Caesar and heir.

His rule begins with yet another Germanic incursion on the provinces of Pannonia, and the Goths invade Moesia (modern-day Serbia and Bulgaria) in the Danube frontier.

His reign sees the true beginning of the crisis of the third century, which will be marked by a series of barbarian invasions across the Danube and internal civil war led by dissident generals.

The Romans finally defeat the invading Goths in 248 after undertaking a series of campaigns against these and other tribes on the Danube, but the legions are not satisfied with the result, probably due to a low share of the plunder, if any.

Rebellion soon arises and Tiberius Claudius Pacatianus is proclaimed emperor by the troops.

He is known from coins, and from mentions in Zosimus and Zonaras, who say that he was an officer in one of the Danube legions.

According to Zosimus, the revolts of Pacatianus in Moesia (he probably controlled Viminacium) and Iotapianus in Syria prompted Philip to make an offer to the Roman Senate to step down, but the senator Gaius Messius Quintus Decius (who was sent by Philip to deal with the rebellion), correctly predicted that Pacatianus the Great would soon be killed by his own men before his own arrival.

After crushing the uprising, Philip nominates Decius as governor of the province, which future events will prove to be a mistake, at least where Philip is concerned.

Pacatianus's revolt had not been the only threat to Philip’s rule: in the East, Marcus Iotapianus had led another uprising in response to the oppressive rule of Priscus and the excessive taxation of the Eastern provinces.

Two other usurpers, Marcus Silbannacus and Sponsianus, are reported to have started rebellions without much success.

The Goths break the peace treaty, renewing their attacks early in 253.

The army is not pleased with the emperor and when Marcus Aemilius Aemilianus, who had replaced Gallus as governor of Moesia Superior and Pannonia, takes the initiative of battle and defeats the Goths in midyear, the soldiers proclaim him emperor.

Valerian’s son and co-emperor Gallienus fights a series of campaigns against the Goths on the Upper Rhine.

While Valerian is fighting against the Sassanid Empire and the Goths, who by this time have sacked Thrace and Asia Minor, Gallienus will be in charge of defending the Roman Empire's border.

In the Western half of the Empire, the situation is difficult.

The Danubian border resists continuous barbarian attacks.

Gallienus has to march with military reinforcements from Gaul towards Dacia and Moesia to fight the barbarians.

The situation is so severe that in 259, the legions of Pannonia and Moesia rebel and choose to make Ingenuus the emperor.

Gallienus reunites the Rhine, leaves a Roman legion their to defend it and goes off to do battle.

Within the borders of the Rhine and the Alps, a Germanic confederation, the Alamanni, who occupy a good part of the Agri Decumates (a region of the Roman Empire's provinces of Germania Superior and Raetia, covering the Black Forest, Swabian Jura, and Franconian Jura areas between the Rhine, Main, and Danube rivers), cross the Alps and attack the fertile plain of the Po river.

The sacking of the area instills terror in Rome, as the city remains unwalled.

The Senate of Rome hastily prepares a crowd of plebs for combat in an attempt to ensure that its shrinking army is capable of protecting the city.

Gallienus had just defeated the pretender Ingenuus when the news arrives of the invasion by the Alamanni.

He marches off with three legions to intercept the barbarians in Italy.

By then, according to the Byzantine historian Joannes Zonaras, the Alamanni had retreated before the unexpected resistance of the citizens of Rome and its Senate.

When Gallienus arrives in the valley of the Po, he finds the Alamanni in the vicinity of Mediolanum, present day Milan.

The victory is total: according to Zonaras three hundred thousand Alamanni fell that day and the emperor received the title Germanicus Maximus.

The Alamanni's success in reaching into the Roman Empire once more reveals the weakness of the centuries-old tradition of posting Rome's legions near the borders without providing for defense within the empire.

The battle of Mediolanum demonstrates to the Romans the value of swift, flexible military units.

Afterward, Gallienus enacts a major reform by introducing a highly mobile field army composed mainly of cavalry (vexillationes).

The main units are under the control of his general, Aureolus, and headquartered in Mediolanum, with the mission to protect Italy.

Finally, the invasion by the Alamanni demonstrates the vulnerability of Italy and especially Rome.

This later causes Emperor Aurelian to have a strong wall built to defend the capital of the Empire.

Gallienus, now reigning alone, faces multiple invasions and several usurpations.

He moves constantly between the Danube and the Rhine, there fighting a series of campaigns against the Goths.

The Holy See had been vacant for nearly a year following the martyrdom of Sixtus II, due yo difficulty in electing a new Pope during the violent persecution which Christians faced.

When the persecution had begun to subside, Dionysius was raised to the office of Bishop of Rome.

Upon his father's capture, Gallienus had put an end to the persecution of the Christians and given the Church legal status, preferring to fight the new religion through intellectual means; to that end, he favors the ancient Greek cults (Demeter of Eleusis) and protects the Neoplatonist philosopher Plotinus.

These initiatives increase the number of his enemies, particularly among the patriotic senators and the Pannonian generals.

Gallienus himself is left in control only of Italy and the Balkans.

Gallienus leads a large Roman force into Moesia to cut off the army of Goths, three hundred and twenty thousand strong, now retreating by land from its plunder of Aegean coastal cities.

The two armies meet at Naissus (modern Niš, Serbia), where the Romans slaughter the Goths by the thousands.

His attention demanded by the revolt of a usurper, Aureolus, in Italy, Gallienus returns there without further pursuit of the survivors, who flee to armed encampments to the northeast.

The Goths are now retreating by land from their plunder of Greece’s Aegean coastal cities into the province of Pannonia, their invasion leading to disaster and even threatening Rome, while the Alamanni, a loosely knit confederation of tribes composed of fragments of several Germanic peoples, are simultaneously raising havoc in the northern part of Italy.

Emperor Gallienus, now fifty, halts the progress of the Alamanni by defeating them in battle in April 268, then turns north and wins several victories over the Goths.

His attention demanded by problems in Italy, Gallienus returns there without further pursuit of the survivors, who flee to armed encampments to the northeast.

In the autumn, he turns on the Goths once again, leading a large Roman force into Moesia to cut off the Gothic army.

Claudius, having succeeded Gallienus as emperor leads the Roman army to victory (although the cavalry commander Lucius Domitius Aurelianus is the real victor) at the Battle of Naissus, where the Romans slaughter the Goths by the thousands in 269.

Large numbers on both sides are killed but, at the critical point, the Romans trick the Goths into an ambush by pretended flight.

Some fifty thousand Goths are allegedly killed or taken captive.

It seems that Aurelian, who was in charge of all Roman cavalry during reign of Claudius, led the decisive attack in the battle.