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.
Caracalla's Parthian War
[4.11.1]  The Parthian's initial replies were of this type, and he declined Caracalla's offer of an alliance. But when the emperor persisted and with many gifts and oaths swore to his enthusiasm for the marriage and his good will toward the Parthians, Artabanus [IV] was won over; addressing Caracalla as his future son-in-law, he promised him his daughter in marriage. When the news was made public, the barbarians prepared for the reception of the emperor of the Romans and rejoiced in the hope of permanent peace.
[4.11.2] Having crossed the riversnote[Euphrates and Tigris. Caracalla reached Arbela, where he destroyed the tombs of the royal house of Adiabene.] unopposed, Caracalla entered the barbarians' land as if it were already his. Sacrifices were offered to him everywhere; the altars were decked with wreaths, and perfumes and every kind of incense were scattered in his path. Caracalla pretended to be delighted by the barbarians' attentions and continued his advance. He had now completed the greater part of his journey and was approaching the palace of Artabanus. The king did not wait to receive the emperor but came out to meet him in the plain before the city, welcoming his son-in-law, the bridegroom of his daughter.
[4.11.3] All the Parthians, crowned with the traditional flowers and wearing robes embroidered in gold and various colors, celebrated the occasion, dancing wildly to the music of flutes and the throbbing of drums. They take delight in such orgiastic dancing, especially when they are drunk.
[4.11.4] Abandoning their horses and laying aside their quivers and bows, the whole populace came together to drink and pour libations. A huge mob of barbarians gathered and stood about casually, wherever they happened to be, eager to see the bridegroom and expecting nothing out of the ordinary.
[4.11.5] Then the signal was given, and Caracalla ordered his army to attack and massacre the spectators. Astounded by this onslaught, the barbarians turned and fled, wounded and bleeding. Artabanus himself, snatched up and placed on a horse by some of his personal bodyguards, barely escaped with a few companions.
[4.11.6] The rest of the Parthians, lacking their indispensable horses, were cut down (for they had sent the horses out to graze and were standing about). They were unable to escape by running, either; their long, loose robes, hanging to their feet, tripped them up.
[4.11.7] Naturally they did not have their quivers and bows with them; what need for weapons at a wedding? After slaughtering a great number of the enemy and taking much booty and many prisoners, Caracalla marched away from the city unopposed. En route he burned the towns and villages and permitted his soldiers to carry off as much as they could of anything they wanted.
[4.11.8] Such was the nature of the disaster which the barbarians suffered when they were not anticipating anything of the kind. After harassing most of the Parthian empire, Caracalla, since his troops were weary by now of looting and killing, went off to Mesopotamia. From there he sent word to the Senate and the Roman people that the entire East was subdued and that all the kingdoms in that region had submitted to him.
[4.11.9] The senators were not unaware of what had actually happened (for it is impossible to conceal an emperor's acts); nevertheless, fear and the desire to flatter led them to vote the emperor all the triumphal honors. Thereafter, Caracalla spent some time in Mesopotamia, where he devoted himself to chariot-driving and to fighting all kinds of wild animals.