Herodian (late second, first half third century): Greek historian, author of a History of the Roman Empire since the Death of Marcus Aurelius in which he describes the reign of Commodus (180-192), the Year of the Five Emperors (193), the age of the Severan dynasty (211-235), and the Year of the Six Emperors (238).
The translation was made by Edward C. Echols (Herodian of Antioch's History of the Roman Empire, 1961 Berkeley and Los Angeles) and was put online for the first time by Roger Pearse (Tertullian.Org). The version offered on these pages is hyperlinked and contains notes by Jona Lendering.
[3.10.1]  When he had settled affairs in the East, Severus returned to Rome, bringing with him his sons, who were then about eighteen years of age.note[Caracalla was eleven, Geta ten.] On the journey he handled provincial problems as each situation demanded, and paid a visit to the troops in Moesia and Pannonia. His trip completed, he was welcomed as "Conqueror" by the Roman people with extravagant praise and adoration.
[3.10.2] He then staged wild-animal shows for the people and celebrated, with merrymaking, holidays, festivals, and spectacles. After distributing lavish gifts and observing the customary festivities associated with a triumph, Severus remained in Rome for a number of years,note[He in fact made a voyage to Tripolitana, where he refounded his native town, Lepcis Magna, and organized the Limes Tripolitanus.] presiding regularly in the courts, attending to civil matters, seeing to his sons' education, and keeping the youths under control.
[3.10.3] But the lads (for they were already young men) were corrupted by the luxury and vice in Rome and by their boundless enthusiasm for shows, dancing, and chariot-driving. The two brothers were contentious from the beginning; as children they had been rivals over quail fights and cockfights, and had had the usual childish quarrels.
[3.10.4] Now their passion for shows and concerts made them constant competitors. Their followers and companions kept them at odds by fawning upon them and urging them to compete in enjoying youthful pleasures. When he was informed of this, Severus tried to reconcile his sons and keep them in hand.
[3.10.5] Before his admission to the imperial ruling company, the elder son had the name Bassianus [Caracalla], but when he had the good fortune to receive the honor of a share in the imperial power, Severus called the youth Antoninus, wishing him to bear the name of Marcus.note[April 202.] He also gave him a wife in the hope that marriage would mature him somewhat; the girl was the daughter of Plautianus, the praetorian prefect.note[The boy's full name was Lucius Septimius Bassianus, but everybody called him Caracalla. Antoninus was, in these days, some sort of title, derived from the name that Marcus Aurelius had given to some of his sons, who were intended successors (Titus Aurelius Antoninus, Titus Aelius Antoninus, Titus Aurelius Fulvus Antoninus). Of course, he called these boys after his predecessor, Antoninus Pius. Caracalla's wife was called Plautilla.]
[3.10.6] As a youth this Plautianus had been a poor man (some say he was banished after being convicted of treason and many other crimes), but he was a fellow countryman of the emperor (Severus was also from Libya) and, as some say, he was related to the emperor; there are those too who charge him with being something worse, saying that when he was in the prime of youth he was the emperor's beloved. Consequently, Severus raised the man from a position of small and negligible honor to a post of great authority; by giving him the property of condemned men, he made Plautianus enormously wealthy. The emperor in fact shared the rule with no one except this man.
[3.10.7] Taking advantage of his authority, Plautianus left no act of violence undone and thus became more feared than any of the prefects before him. Severus united the two families by the marriage of his son to the daughter of Plautianus.
[3.10.8] But Caracalla took no pleasure at all in this union, since he had married by compulsion, not by choice. He was exceedingly hostile to the girl, and to her father too, and refused to sleep or even eat with his wife; the truth is that he loathed her and daily promised to kill her and her father as soon as he became sole ruler of the empire.note[This happened in fact when Caracalla succeeded his father in 211.] She reported these threats to her father and aroused his fury by stories of her husband's rancor.