Caracalla (ə/; Latin: Marcus Aurelius Severus Antoninus Augustus; 4 April 188 – 8 April 217), formally known as Antoninus, ruled as Roman emperor from 198 to 217 AD. He was a member of the Severan dynasty, the elder son of Septimius Severus and Julia Domna. Co-ruler with his father from 198, he continued to rule with his brother Geta, emperor from 209, after their father's death in 211. He had his brother killed later that year, and reigned afterwards as sole ruler of the Roman Empire. Caracalla's reign featured domestic instability and external invasions by the Germanic peoples.
Caracalla's reign became notable for the Antonine Constitution (Latin: Constitutio Antoniniana), also known as the Edict of Caracalla, which granted Roman citizenship to nearly all free men throughout the Roman Empire. The edict gave all the enfranchised men Caracalla's adopted praenomen and nomen: "Marcus Aurelius". Domestically, Caracalla became known for the construction of the Baths of Caracalla, which became the second-largest baths in Rome; for the introduction of a new Roman currency named the antoninianus, a sort of double denarius; and for the massacres he enacted against the people of Rome and elsewhere in the empire. In 216, Caracalla began a campaign against the Parthian Empire. He did not see this campaign through to completion due to his assassination by a disaffected soldier in 217. Macrinus succeeded him as emperor three days later.
The ancient sources portray Caracalla as a tyrant and as a cruel leader, an image that has survived into modernity. Dio Cassius (c. 155 – c. 235) and Herodian (c. 170 – c. 240) present Caracalla as a soldier first and as an emperor second. In the 12th century, Geoffrey of Monmouth started the legend of Caracalla's role as the king of Britain. Later, in the 18th century, the works of French painters revived images of Caracalla due to apparent parallels between Caracalla's tyranny and that ascribed to Louis XVI of France (r. 1774–1792). Modern works continue to portray Caracalla as a psychopathic and evil ruler, painting him as one of the most tyrannical of all Roman emperors.
Caracalla was born Lucius Septimius Bassianus. He was renamed Marcus Aurelius Antoninus at the age of seven as part of his father's attempt at union with the families of Antoninus Pius and Marcus Aurelius. According to the 4th century historian Aurelius Victor in his Epitome de Caesaribus, he became known by the agnomen "Caracalla" after a Gallic hooded tunic that he habitually wore and made fashionable. He may have begun wearing it during his campaigns on the Rhine and Danube. Dio generally referred to him as Tarautas, after a famously diminutive and violent gladiator of the time.