Gaius Messius Quintus Decius was born around the year AD 190 in a village called Budalia near Sirmium. He wasn't however from simple beginnings, as his family had influential connections and also had possession of considerable tracts of land.
When emperor Philippus Arabs, fearing the collapse of the empire in face of rebellions and barbarian invasions, spoke to the senate in AD 248 offering his resignation, it was Decius, then city prefect of Rome, who dissuaded him to stay in power, forecasting that the usurpers would surely soon die at the hands of their own troops.
Shortly afterwards Decius accepted a special command along the Danube to drive out the invading Goths to and restore order among the mutinous troops. He did as he was bid in very short time, proving himself a very able leader.
Decius was forced to act and took his Danubian troops, traditionally the best of the empire, on a march southwards. The two forces met in September or October AD 249 at Verona, where Philippus' larger army was defeated, leaving Decius sole emperor of the Roman world.
The senate confirmed him as emperor on his arrival at Rome. On this occasion Decius adopted the name Trajanus (hence he is often referred to as 'Trajanus Decius') as an addition to his name as a sign of his intention to rule in similar fashion to the great Trajan.
In AD 250 news reached the capital of a large-scale crossing of the Danube by the Goths under the leadership of their able king Kniva. At the same time the Carpi were once again attacking Dacia. The Goths divided their forces. One column moved into Thrace and besieged Philippopolis, while king Kniva moved eastwards. The governor of Moesia, Trebonianus Gallus, though managed to force Kniva to pull back. Though Kniva was not yet done, as he went on to besiege Nicopolis ad Istrum.
Decius gathered his troops, handed government to a distinguished senator, Publius Licinius Valerianus, and moved to drive the invaders out himself (AD 250). Before leaving he also proclaimed his Herennius Etruscus Caesar (junior emperor), assuring an heir was in place, should he fall whilst campaigning.
The young Caesar was sent ahead to Moesia with an advance column whilst Decius followed with the main army. At first all went well. King Kniva was driven from Nicopolis, suffering heavy losses, and the Carpi were forced out of Dacia. But while trying to drive Kniva out of Roman territory altogether, Decius suffered a serious setback at Beroe Augusta Trajana.
Titus Julius Priscus, governor of Thrace, realized the siege of his provincial capital Philippopolis could hardly be lifted after this disaster. As an act of despair he tried to save the city by declaring himself emperor and joining with the Goths. The desperate gamble failed, with the barbarians sacking the city and murdering their apparent ally.
Leaving Thrace to the devastation of the Goths, the emperor withdrew with his defeated army to join with the forces of Trebonianus Gallus.
Though soon the emperor was to learn of a new usurper. This time, in early AD 251, it was Julius Valens Licinianus (in Gaul, or at Rome itself), who enjoyed considerable popularity and acted apparently with the support of the senate. But Publius Licinius Valerianus, the man Decius had especially appointed to oversee matters of government back home in the capital put down the rebellion. By the end of March Valens was dead.
But in June/July AD 251 Decius too met his end. When king Kniva pulled out of the Balkans with his main force to return back over the Danube he met with Decius' army at Abrittus. Decius was no match for the tactics of of Kniva. His army was trapped and annihilated. Both Decius and his son Herennius Etruscus were killed in battle.
The senate deified both Decius and his son Herennius shortly after their deaths.