Cniva
Cniva was a Gothic king who invaded the Roman Empire in the middle of the 3rd century AD. His regnal years are uncertain. He successfully captured the city of Philippopolis in 250 and killed Emperor Decius and his son Herennius Etruscus at the Battle of Abritus as he was attempting to leave the Empire in 251. This was the first time a Roman Emperor had been killed in combat against foreigners. He was allowed by the new Emperor Trebonianus Gallus to leave with his spoils and was paid tribute to stay out of the empire.
Invasion of Moesia
Cniva began the invasion of the Roman Empire when he crossed the Danube. He sent detachments throughout the Roman province of Moesia with forces of Goths and Sarmatians. His considerable forces demanded the attention of the emperor Decius.The first column of Cniva's army, a detachment of about 20,000 likely led by the chieftains Argaith and Gunteric, besieged Marcianopolis, apparently without success. They probably then headed south to besiege Philippopolis. Cniva's main column under the King himself crossed the Danube at Oescus then headed eastwards to Novae, where he was repelled by the provincial governor Trebonianus Gallus. The invaders then headed south to plunder Nicopolis ad Istrum where Decius defeated them but not decisively. After these initial setbacks, the Goths moved southwards through the Haemus mountain and Decius pursued them to save Philippopolis. This time Decius' army was taken by surprise while resting at Beroe/Augusta Traiana. The Romans were heavily defeated in the ensuing battle. Decius was forced to withdraw his army to the north at Oescus, leaving Cniva ample time to ravage Moesia and finally capture Philippopolis in the summer of 251, in part with the help of its commander, a certain Titus Julius Priscus who had proclaimed himself Emperor. It seems that Priscus, after receiving the news of the defeat at Beroe, thought that the Goths would spare him and the city. He was wrong and was probably killed when the city fell. Then the invaders began returning to their homeland, laden with booty and captives, among them many of senatorial rank.
The sack of Philippopolis invigorated Decius, who intercepted several parties of Germans, and repaired and strengthened his fortifications along the Danube, intending to oppose Cniva’s forces.