December 19 – Geta is lured to come without his bodyguards to meet Caracalla, to discuss a possible reconciliation. When he arrives the Praetorian Guard murders him and he dies in the arms of his mother Julia Domna.
Emperor Caracalla leaves Rome and expels some German marauders from Gaul. He defends the northern Rhine frontier against the Alamanni and the Chatti. Caracalla wins a victory over the German tribes on the banks of the River Main, and gives himself the title "Germanicus". It is probably while campaigning in Germania that he takes a liking to the caracalla, a Celtic or German tunic from which he acquires the name by which he is known.
Cao Cao, the prime minister of the Han dynasty, is titled Wei Gong (Duke of Wei) and given a fief of ten cities under his domain. This later becomes the Kingdom of Wei.
Caracalla's troops massacre the population of Alexandria, Egypt, beginning with the leading citizens. The emperor is angry about a satire, produced in Alexandria, mocking his claim that he killed Geta in self-defense.
Caracalla introduces a new coin, the Antoninianus. The weight of this coin is a mere 1/50 of a pound. Copper disappears gradually, and by the middle of the third century, with Rome's economy in crisis, the Antonianus will be the only official currency.
The silver content of the Roman denarius falls to 43 percent under emperor Elagabalus, down from 50 percent under Septimius Severus, as he empties the treasury with his excesses while his grandmother, Julia Maesa, rules the Empire.