AR Antoninianus, A.D. 250-251 (as Caesar), Rome, 22.0mm, 3.08g, 180°, RIC IV 138; scarce.
Obv: Q HER ETR MES DECIVS NOB C. Radiate draped bust right.
Rev: CONCORDIA AVGG. Clasped hands.
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Quintus Herennius Etruscus Messius Decius Augustus was Roman emperor in 251, in a joint rule with his father Decius. Herennius was born in near Sirmium in Pannonia (now Serbia), during one of his father's military postings. His mother was Herennia Cupressenia Etruscilla, a Roman lady of an important senatorial family. Herennius was very close to his father and accompanied him in 248, when Decius was appointed by Philip the Arab to deal with the revolt of Pacatianus in the Danube frontier. Decius was successful in defeating this usurper and felt confident to begin a rebellion of his own in the following year. Acclaimed emperor by his troops, Decius marched into Italy and defeated Philip near modern Verona. In Rome, Herennius was declared heir to the throne and received the title of Princeps Iuventutis (prince of youth). At the beginning of 251, Decius elevated Herennius to the title of Augustus making him his co-emperor.

The father and son, now joint rulers, embarked in an expedition against King Cniva of the Goths to punish the invaders for raids they had been engaged in across the Danubian frontier. Cniva and his men were returning to their territory, when they encountered the Roman army. Showing a very sophisticated military tactic, Cniva divided his army in smaller, more manageable groups and started to push back the Romans into a marshy swamp. Sometime during the first two weeks of June they engaged in the battle of Abrittus. Herennius died in battle, struck by an enemy arrow. Decius survived the initial confrontation, only to be slain with the rest of the army before the end of the day. It was the first time that two emperors were killed in the same confrontation. With the news of the death of the emperors, the army proclaimed Trebonianus Gallus emperor, but in Rome they were succeeded by Hostilian, who would die shortly afterwards in an outbreak of plague.