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.
Massacre in Alexandria
[4.9.1]  When they saw what the emperor was doing, the people rejoiced and celebrated, making merry the whole night long, but they did not know his secret intent. In all his actions Caracalla was playing the hypocrite; his true plan was to destroy most of them. The source of the enmity he was concealing was this.
[4.9.2] While he was still living in Rome, both during his brother's lifetime and after his murder, it was reported to him that the Alexandrians were making endless jokes about him. The people of that city are by nature fond of jesting at the expense of those in high places. However witty these clever remarks may seem to those who make them, they are very painful to those who are ridiculed.
[4.9.3] Particularly galling are quips that reveal one's shortcomings. Thus they made many jokes at the emperor's expense about his murdering his brother, calling his aged mother Jocasta, and mocking him because, in his insignificance, he imitated the bravest and greatest of heroes, Alexander and Achilles. But although they thought they were merely joking about these matters, in reality they were causing the naturally savage and quick-tempered Caracalla to plot their destruction.
[4.9.4] The emperor therefore joined the Alexandrians in celebrating and merrymaking. When he observed that the city was overflowing with people who had come in from the surrounding area, he issued a public proclamation directing all the young men to assemble in a broad plain, saying that he wished to organize a phalanx in honor of Alexander similar to his Macedonian and Spartan battalions, this unit to bear the name of the hero.
[4.9.5] He ordered the youths to form in rows so that he might approach each one and determine whether his age, size of body, and state of health qualified him for military service. Believing him to be sincere, all the youths, quite reasonably hopeful because of the honor he had previously paid the city, assembled with their parents and brothers, who had come to celebrate the youths' expectations.
[4.9.6] Caracalla now approached them as they were drawn up in groups and passed among them, touching each youth and saying a word of praise to this one and that one until his entire army had surrounded them. The youths did not notice or suspect anything. After he had visited them all, he judged that they were now trapped in the net of steel formed by his soldiers' weapons, and left the field, accompanied by his personal bodyguard. At a given signal the soldiers fell upon the encircled youths, attacking them and any others present. They cut them down, these armed soldiers fighting against unarmed, surrounded boys, butchering them in every conceivable fashion.
[4.9.7] Some did the killing while others outside the ring dug huge trenches; they dragged those who had fallen to these trenches and threw them in, filling the ditch with bodies. Piling on earth, they quickly raised a huge burial mound. Many were thrown in half-alive, and others were forced in unwounded.
[4.9.8] A number of soldiers perished there too; for all who were thrust into the trench alive, if they had the strength, clung to their killers and pulled them in with them. So great was the slaughter that the wide mouths of the Nile and the entire shore around the city were stained red by the streams of blood flowing through the plain. After these monstrous deeds, Caracalla left Alexandria and returned to Antioch.