Cniva (Kniwa, meaning "knife") (flourished mid-3rd century CE) was the Gothic chieftain who invaded the Roman Empire in the third century CE. He successfully conquered the city of Philippopolis, present-day Bulgarian city Plovdiv, and killed the emperor Decius and his son Herennius Etruscus at the Battle of Abrittus as he was attempting to leave the Roman Empire. He was allowed 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, Germans[dated info] and Sarmatians. His considerable forces demanded the attention of the emperor Decius. While Cniva was laying siege to the city of Nicopolis, Decius arrived, and the Goths left and headed towards Philippopolis. Decius and his troops pursued Cniva through the difficult terrain, but soon, after many forced marches, Cniva turned his troops on Decius, who thought he was further away from the Goths. The Roman camp was surprised and Decius fled while his army was defeated. Then Cniva laid siege to Philippopolis and, after a long resistance, he conquered the city, slaying one hundred thousand people, and taking many prisoners.
Decius’s response 
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. The Romans in time, with their superior numbers, surrounded the Goths, who attempted now to retreat from the empire. But Decius, seeking revenge and confident of victory, attacked the Goths at a small town called Forum Terebronii. The Roman army was caught in a swamp when they attempted to attack the Gothic army, and both the emperor Decius and his son Herennius Etruscus were slain in this battle, known as the Battle of Abrittus.
Terms of peace 
After the battle, the new emperor, Trebonianus Gallus, let Cniva leave with his spoils, and aided the Goths' departure. He even promised to pay a tribute to Cniva in order to keep him from invading the empire again.
- Edward Gibbon, History of the Decline and Fall of the Roman Empire, Chapter 10.