Acacius, son of Archelaus () was a Byzantine official, mentioned as a representative of emperor Justin II (r. 565–578) in 573. He is known for causing a military disaster in a siege of Nisibis (573), early in the Roman–Persian War of 572–591.
Siege of Nisibis
John of Epiphania
Acacius is first mentioned by name in the work of John of Epiphania. He was reportedly sent by Justin II to dismiss Marcian, the magister militum per Orientem, from office. Acacius dutifully did so, preventing Marcian from concluding the siege of Nisibis. The leaderless Byzantine troops retreated. After the winter season, Marcian gathered together his forces again and set out from Dara meeting with the barbarians in front of the city of Nisibis led by Varaman, who was in command of the companies stationed them. A fierce battle followed in which the Romans turned the barbarians to flight vigorously near the Persian place called Sarmathon, bringing down many of them. Then making an attempt at the fortress of Thebython where they spent ten days. Unable to seize it, they returned to the city of Dara while it was still spring and again invaded enemy land planning to besiege Nisibis with the approval of the emperor Justin."
"While they were encamped near the city, King Chosroës set out from Babylon with an army of Medians crossing the Tigris River and passing over empty land, as the Roman had not heard of the king‘s movements, and came upon the Persian fortress of Amvaron (it is five days distant from the city of Circesion), where he dispatched Adaarman, as the general was called, to cross the Euphrates River there and plunder Roman territory with thousands of his own Medians and nomadic barbarians. At the same time, he urged Avorras on to the Romans besieging Nisibis. When Adaarman reached the city of Circesion, he crossed the Euphrates and began to forage Roman lands without any restraint. For due to the previous peace and quiet that they had enjoyed during the reign of Justinian, their war time preparation had receded and their virility completely vanished. As no one dared to come to blows with the barbarians, Adaarman was able to come as far as the city of Antioch ravaging the sites and fields near the city and then advancing on Coele Syria. He made camp not far from the great city of Apamea, to whose citizens’ embassies he promised to enter the city and leave it unharmed, but then actually entering it where the Persians seized their possessions, enslaved its inhabitants, and put the entire city to the flame then returning in all haste to their own land. As a result of these actions, the emperor Justin dispatched Acacius (the Romans are accustomed to add the name of Archelaus) removing Marcian, who was still besieging Nisibis, from office because he had doubts about his loyalty, as the city had not yet been taken control of. ... As the Romans were retreating."
John of Ephesus
John of Ephesus gives a similar account, but gives more attention to the contact of Acacius and the reactions of the soldiers: "The illustrious Patrician Marcian, a relative of king Justin, was sent by him to command one of the Roman armies in the east; and being warmly zealous for the polity of the Christians, he assembled an army, and laid siege to Nisibis, the frontier town and bulwark of Mesopotamia, and then in possession of the Persians. And having strongly invested it, and constructed round it a palisade, he commenced, with the aid of the skilful mechanicians whom he had brought with him, to erect more scientific works, consisting of lofty towers and strong covered approaches. And the city began to be distressed, and both its inhabitants and the Persian garrison despaired of their lives when they saw it so hard pressed by the Romans. And as those inside were in alarm, so those outside were making their preparations to assault the city and plunder it; but just as they were ready to storm it, a violent tempered man arrived, named Acacius Archelaus, sent for no just reason by king Justin to deprive Marcian of his command, and cut his girdle and send him away from the cast."