Roman Legionaries: From what we can tell Lorica Segmentata gradually dropped out of use in the 3rd C and probably never really caught on in the east where both scale and mail were more common. Helmet styles also varied. The Spangenhelm styles seemed to be of Danubian origin so may have been quite common at the end of the third century up to the time of Constantine and beyond when the bulk of good Roman troops were of Illyrian origin. The mobile field army would have been resupplied from a variety of locations so I can imagine quite a bit of variation within any given unit whereas garrison troops would have been more uniform. For what it is worth here is my interpretation of a veteran 4th century unit with a combination of spangenhelms and ridge helmets, some replacement shields picked up off the battlefield and a mix of scale and mail armour with some unarmoured back rankers. It represents two units of Auxilia Palatina which were raised by Constantine and were deployed in pairs.
The conflict between Constantine and Licinius was not just political, but also religious – so the preparations for this war were not only material, but also spiritual. Thus, the forces of each emperor openly exhibited their religious affiliations. Constantine had removed pagan insignia and rites from his armies shortly after his conversion, and he had replaced them with Christian symbols and trappings. The emperor wore a helmet emblazoned with the Christogram, and his soldiers carried shields marked with the same sign. An honor guard of fifty men distinguished for their personal courage and Christian piety carried the Labarum at the front of Constantine’s troops, and employed it as a magic talisman against his enemies. The emperor had a special tent shaped like a cross in which he prayed to the Christian Deity for inspiration before battles. And Catholic clergy accompanied the troops to assist in devotions and to pray for victories.
While Licinius had employed a syncretistic “Highest God” prayer and allowed some religious toleration in his armies after the “Edict of Milan,” he had early identified Jupiter as his special divine patron, and had gradually reintroduced mandatory pagan rites in his military camps during his “cold war” with Constantine. The forces which Licinius assembled for the final conflict with his enemy were completely pagan in outward appearance. His military insignia included pagan designs, and his army camps contained pagan altars. Priests and soothsayers carried out traditional sacrifices and rites to obtain the help of the old gods. And prior to his first battle with Constantine, Licinius gathered his bodyguard and commanders together in a sacred grove for divine sacrifices, and declared that the outcome of the coming conflict would determine which emperor was correct in his religious policy, and which deity was the supreme power in the universe. Thus, the second civil war between Constantine and Licinius can rightfully be called a “religious crusade” or a “holy war” between classical paganism and the Christian religion.
This climactic war would take place during the summer of 324, and would involve the combatants in several battles fought at the eastern tip of Europe, the western edge of Asia, and in the waters between the two continents In June, Constantine led his land army from Macedonia northeastward into Thrace, while Crispus followed with the fleet eastward across the Thracian part of the Aegean Sea. Late in the month, Constantine arrived at the outskirts of Hadrianople (Edirne). The topography around the city offers a strong defensive position against an attack from the west. Hadrianople is located on the southwestern flank of a steep mountain which rises above the confluence of two rivers to the south of it. The smaller Tonoseius (Tunca) River flows from the north of Thrace (Bulgaria), and passes along the western side of the city until it turns east beneath it and runs into the larger Hebrus (Meriç) River. The latter flows from the northwest of Thrace, and passes along the southern side of the city where it receives the Tonoseius; then the enhanced Hebrus flows southward into the Thracian Sea above the island of Samothrace (the southern part of the river is the boundary between European Turkey and Greece today). In order to gain control of Thrace and of the plains stretching from Hadrianople to the Bosporus Strait, Constantine had to cross the Hebrus River and take the mountain above the city. However, Licinius had gotten there first, and, as the Origo recorded, “had filled up the sides of the steep mountain at Hadrianople with a huge army” arrayed in long battle lines. Constantine established his camp on the southwestern side of the Hebrus River, and planned a battle strategy which would overcome the better position and larger forces of his enemy. For several days he assembled his troops in battle formation as if he were going to have them charge across the river in a direct frontal assault against the Licinian army. But then he created a diversion by having the soldiers at one end of his lines cut down trees and pretend that they were building a bridge for a safer crossing. While this action distracted the Licinian forces, Constantine hid 800 of his best cavalry and 5,000 infantry and archers in a thick forest at the other end of his lines. On the morning of 3 July, the emperor led these men out of the forest and across a fordable section of the Hebrus River in a surprise attack against a side wing of the enemy lines. This maneuver threw the Licinian army into confusion, and allowed the rest of the Constantinian troops to ford the river en masse and drive the enemy lines back up the steep mountain above Hadrianople. During the course of the battle, Constantine directed the special Labarum guard to move the sacred Christian talisman to any area where his soldiers seemed to be faltering. This seemed to embolden his troops and to frighten the Licinian forces. Late in the day, Constantine led a cavalry charge in which he was wounded in the thigh, but by which he broke the last resistance of the enemy. Licinius retreated eastward through Thrace, but left over 30,000 of his troops dead on the battlefield according to Zosimus. Constantine took the enemy camp at Hadrianople, and received the surrender of thousands of the soldiers who had been left behind by the hasty flight of their commander. The astute military strategy and the potent Christian signs of Constantine had won the first battle in the crusade to free the suffering east from its “savage beast” (Ill. 53).
Licinius retreated 150 miles southeast to Byzantium on the Bosporus Strait. He kept a few thousand of the troops he had led away from the defeat at Hadrianople with him in this well-fortified town at the eastern tip of Europe; and he had the rest of his forces ferried across the Bosporan waters to his western Asian domains. Licinius hoped that he would be able to block Constantine at the Bosporus while his admiral Abantus would be able to stop Crispus in the Hellespont. If either part of this fall-back strategy failed, he would have a land army awaiting him in Bithynia. After gaining control of Hadrianople, Constantine pursued Licinius through Thrace, and directed Crispus to break the blockade in the Hellespont and meet him at Byzantium. By the middle of the summer, the army of Constantine reached the outskirts of this old Greek colony which was located on a promontory at the southern end of the Bosporus Strait. The emperor had an earth ramp built up against a part of the land wall of the city, and then had a wooden tower moved up to the top of this ramp. He had some of his troops throw missiles down upon the defenders of the city from the tower, while he had others push battering rams and siege engines up against the rest of the walls. These actions soon made Licinius realize that a prolonged stay in Byzantium was not possible. While Constantine was directing the siege at Byzantium, Crispus was breaching the blockade in the Hellespont. He made an astute decision to enter the narrow waters of the strait with a small fleet of eighty ships. Abantus opposed this entry with a large armada of 200 ships with which he felt he could easily surround and defeat the enemy forces. Yet, the large numbers and confined conditions of the Licinian navy worked to the advantage of Crispus, who was able to outmaneuver, hit, and sink many of the opposing ships. Abantus sailed back to the east end of the Hellespont to regroup his forces while Crispus brought in the remainder of his ships. On the next day near Callipolis (Gallipoli), the two fleets met each other for a final battle. Hard winds blew many of the Licinian ships against rocks, and allowed Crispus to win a total victory over his adversary. Abantus lost his own vessel, and barely escaped by swimming to the shore. All but four of the Licinian ships were destroyed or captured in the two naval battles in the Hellespont Strait. Crispus loaded provisions that he knew Constantine needed for the siege at Byzantium, and then sailed through the Sea of Marmora to join his father at the Bosporus Strait. When Licinius saw the Constantinian fleet approaching, and knew that he would soon be blockaded by sea as well as by land, he decided to retreat to Bithynia. He abandoned Byzantium, and sailed across the Sea of Marmora to Chalcedon (Kadiköy). Here, he reorganized his army, raised more forces – including even Gothic mercenaries, and worked to secure the northern section of his Asian domains. He also promoted his Master of Offices Martinianus to the rank of Augustus, and dispatched him to secure the southern section of the Asian coast to the Hellespont. Meanwhile, Constantine entered Byzantium by land and Crispus reached it by sea. The proud father and his son shared stories of their victories, and made plans for their final push against Licinius in Asia.
In early September, Constantine transported his army up the Bosporus Strait to the mouth of the Black Sea. He landed his forces on the Asian side of the strait at a place called the Sacred Promontory. He drew up his battle formations, and marched south against his enemy. In the meantime, Licinius had assembled as large an army as he could at Chalcedon. He still had a significant portion of his forces from Thrace. Martinianus had brought up soldiers stationed on the Asian side of the Hellespont; and a contingent of Gothic troops under their chieftain Alica had joined him. When he learned that Constantine was approaching, he advanced a couple of miles north toward Chrysopolis (Üsküdar – an Asian suburb of modern Istanbul at the bottom of the Bosporus Strait) to make his stand. Constantine had already arrived, and had set up his prayer tent to seek divine guidance for the coming conflict. On 18 September, Licinius drew up his battle lines with the images of the pagan gods placed among them. However, through previous defeats, he had developed a superstitious fear of the Christian Labarum of Constantine, and bid his men not to look at or attack it directly. After gaining the inspiration he needed, Constantine emerged from his tent and ordered his troops to make a direct frontal assault upon the enemy. In a single decisive charge, the forces of Constantine mowed down the soldiers of Licinius, leaving 25,000 of them dead on the field at Chrysopolis (Ill. 54). After this horrible defeat, Licinius fled east to Nicomedia. There, he was persuaded by his wife Constantia that further resistance was useless, and was heartened by her offer to seek leniency for him. On the following day, Constantia went to the camp of her brother, and offered the surrender and abdication of both Licinius and Martinianus if their lives would be spared. Constantine accepted, and later in the day received the purple garments from the deposed rulers, and was saluted by them as the sole Augustus over the Roman Empire. Constantine sent Licinius to Thessalonica and Martinianus to Cappadocia under guard for forced retirements. Through suspicion of treasonable actions and at the request of the army command, both were put to death the following year to save the state from more war.