Caracalla left Nicomedia in April, after having held gladiatorial games in honour of his birthday (which was 4 April). He moved on to Antiochia, where according to Cassius Dio he indulged in luxurious living. At the end of the summer the emperor reached Alexandria, probably the second or third city of the Empire and once founded by Alexander the Great himself. The emperor made his quarters in the precinct where the Serapaeum, the sanctuary devoted to the Hellenistic god Serapis, was located. One of the purposes of his journey to Alexandria was to see the temple dedicated to this god. The other was to visit Alexander’s tomb, the tomb that had been closed to the public some 15 years previously by Caracalla’s father Septimius Severus.
The citizens of Alexandria had enthusiastically welcomed their emperor. Yet they had also greatly angered him for some reason. It is hard to tell what they had done exactly, but apparently they had made jokes about his involvement in Geta’s murder. Herodianus claims they had also called his mother Julia Domna “Jocasta”, referring to Oedipus’ mother and the rumours about an incestuous relationship between Caracalla and his mother. These stories about Julia – also mentioned in the Historia Augusta – were most likely fabricated. In any case, the emperor was furious.
According to Herodianus, he issued an edict, ordering all the young men of the city to gather at a designated square. There he was to form them into a Macedonian phalanx to honour Alexander the Great. Herodianus writes that:
“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. 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.”
It was carnage. The soldiers easily killed their unarmed victims and buried them in mass graves. Cassius Dio has a different, less detailed version in which Caracalla invites the leading citizens of Alexandria to a banquet and then kills them. After the murders, he sends his soldiers into the streets to slaughter anyone they meet. Although it does seem likely Caracalla had many Alexandrians killed, it is simply not plausible that he massacred the whole city. Alexandria continued to be one of the most important cities of the Empire.
– Adrian Goldsworthy, The Fall of the West, p. 74.