Cniva in the context of Decius

Quintus Herennius Etruscus Messius Decius (died c. June 251), known simply as Herennius Etruscus, was briefly Roman emperor in 251, ruling jointly under his father Decius. His father was proclaimed emperor by his troops in September 249 while in Pannonia and Moesia, in opposition to Philip. Decius defeated Philip in battle, and was then proclaimed emperor by the Senate. Etruscus, still a child, was elevated to Caesar (heir) in 250, then further raised to Augustus (emperor) in May 251. When the Goths, under Cniva, invaded the Danubian provinces, he was sent with a vanguard, followed by the main body of Roman troops, led by Decius. They ambushed Cniva at the Battle of Nicopolis ad Istrum in 250, routing him, before being ambushed and routed themselves at the Battle of Beroe. Etruscus was killed in the Battle of Abritus the following year, alongside his father. After the deaths of both emperors, Trebonianus Gallus, who had been governor of Moesia, was elected emperor by the remaining Roman forces.

The Battle of Abritus also known as the Battle of Forum Terebronii occurred near Abritus (modern Razgrad) in the Roman province of Moesia Inferior in the summer of 251. It was fought between the Romans and a federation of Gothic and Scythian tribesmen under the Gothic king Cniva. The Roman army was soundly defeated, and Roman emperors Decius and Herennius Etruscus, his son, were both killed in battle. It was one of the worst defeats suffered by the Roman Empire against the Germanic tribes, rated by the Roman historian Ammianus Marcellinus as on par with the Battle of the Teutoburg Forest in 9, the Marcomannic invasion of Roman Italy in 170, and the Battle of Adrianople in 378.

The emperors' deaths led to more political instability at Rome; and the loss of the army allowed repeated barbarian incursions in the region for the next two decades.

The Gothic War of 248–253 took place between the years 248 and 249, as well as in the year 253. Within this war, a series of battles occurred and plundering was carried out by the Goths and their allies in the eastern territory of the Roman Empire, specifically in the Balkans. With the cessation of the payment of tribute previously made by the Roman emperor Philip the Arab (r.  244–249) to the tribes beyond the Danube, the Goths and their allies, led by King Ostrogotha and his subcommanders Argedo and Gundericus, moved towards the Roman border and began a series of attacks, including against the fortified city of Marcianopolis (today Devnya) in Thracia. After these actions, the Goths withdrew with their spoils of war.

In 250, the invasions continued, the Carpiani attacked Dacia, while the Gothic King Cniva commanding various groups of Goths and other allied peoples, defeated the Romans in two major battles, in one of these he killed the Roman emperor Decius (r.  249–251) and his co-emperor Herennius Etruscus (r.  251). The imperial successor Trebonianus Gallus (r.  251–253) pledged to pay an annual tribute if the invaders left, however, he did not keep his promise, which provoked new attacks in 253, although the governor and future emperor Aemilianus (r.  253) managed to stop these raids.

The Battle of Nicopolis ad Istrum was fought between the Roman army of Emperor Decius and his son Herennius Etruscus, and the Gothic army of King Cniva, in 250. The Romans were victorious.

The Battle of Beroe was a conflict near Stara Zagora, ancient Ulpia Augusta Traiana, between the Romans and Goths in 250. The Romans under Trajan Decius were pursuing the Goths, under Cniva, after their victory at the Battle of Nicopolis ad Istrum. A Goth ambush at Beroe led to heavy Roman losses and forced Decius to retreat across the Balkan Mountains to Moesia. This allowed Cniva to capture Philippopolis in Thrace.

Ostrogotha was a leader of the Goths in Ukraine, who invaded Roman Moesia during the Crisis of the Third Century. He was a contemporary of Cniva, who also led Gothic armies in the same period.

He was mentioned by the 6th-century historian Jordanes in his history of the Goths. Cassiodorus, who Jordanes reported to be the main source upon which he based his own work, also mentioned Ostrogotha as one of the ancestors of Amalasuintha and her father, Theoderic the Great.