Because why write in the old thread where I can't make corrections when I can post here?
Anyways: Inspired by Zuvarq's old TL and by Jaydoh's Cadavera Vero Innumera, this TL starts at the the end of the Classical age. As with all of my TL's, some of the action takes place beforehand, with butterflies before the reign of Constantine (mainly within the Church). The specific point of departure is in butterflying the immigration of the Ghassanids to the Levant. They instead cause upheavals in Arabia. Later changes include a stronger Arianism in the east and in parts of North Africa, and with Constantine the Great being the last Emperor of a unified empire.
This is the reworked first update:
The Constantinian Civil War
Constantine the Great had been a transformative emperor- he legalized and then made official the Christian faith, back during the brief days before the Great Schism. He was military successful and afforded the empire stability after the collapse of the Tetrarchy. To Christians, he was the man who accepted the Lord and ended years of persecution. He reformed the monetary system, reformed the government, and built a grand new capital, Constantinople, the City of the World's Desire. And he had avoided the pitfalls of non-dynastic succession.
But, for all the man's greatness and, to some, holiness, his work would be undone after his death. He was the first Christian emperor, but was also the last man to rule the entire unified Roman Empire. His legacy in the East is untarnished- his successor there continued his reforms, and largely avoided the disasters of invasion and war that befell his Western counterparts.
Crispus, stalwartly ignoring the chaos occurring to his west, instead focused on fighting the Persians and, on the domestic front, continuing his father's reforms and cementing Arian religious dominance. Shapur II had declared war soon after Crispus arrived in the East, and the Goths were causing disturbances on the Danube border; Crispus would therefore remain uninvolved in the civil war between his brothers.
These brothers received much smaller (and relatively poorer) lands compared to the east- the entirety of the west was split into three. Constans, dominated by barbarian officers and other favorites, based himself out of Toletum in Spain. The strategy of his officers was largely one of biding time and striking through Aquitaine after the other two factions bloodied each other. Constans controlled Hispania, Mauretania and Africa- the control of the grain trade would bolster his position considerably.
Constantine, the devout Nicene partisan counterpart to Crispus' Arian zeal in the East, controlled Italy and Illyria. He had the support of Christians and of the city of Rome, backed up by the smaller Illyrian and Italian legions. His strategy was cautious, although not to the degree of his brother Constans. Instead, Constantine operated out of the city of Ravenna, hoping to trap the rash Constantius' armies in northern Italy.
Constantius controlled, like his namesake, Britannia and Gaul. He denuded the island of troops, stripping defense to the barebones in order to go crush Constantine and then Constans (and, if sources are to believed, Crispus as well). Constantius was, of the four sons, the least Christian- he practiced rudimentary Christian practices, but was largely considered to be a crypto-pagan. He, of his brothers, was also the boldest, and he would use the legions he had to conquer Rome. He also had pagan allies. Whereas Constans' elites were to some extent Romanized, Constantius married his natural daughter to the son of the leader of the Salian Franks, who would cross the Rhine in exchange for the promise of land. Scholars believe that, if Constantius had prevailed, they might have become the primary guard of the Rhine.
The civil war would last five years, taxing the lands of the West to the breaking point. Constantius' early foray into northern Italy was stopped before the Po by Constantine, who won a Pyrrhic victory near the town of Mantua during Constantius' retreat from Italy in 342. By this time, Constans had constricted grain purchases, and Constantine made an ill-considered move to attack Africa, thinking that Constantius might instead cross the Pyrenees. This attack on Africa was crippled by storms and a fire among the ships- Constans' forces won a battle off the coast of Carthage, and then landed the Mauretanian "legions" on Sicily in order to occupy that island. Constantius had come back south in early 343, crossing the Po and winning yet another battle near the city of Pisa in the summer of that year. The rest of 343 was spent battling small forces to their north, unwilling to go besiege Rome and fight the remainder of Constantine's armies at the time.
Constantius would then, however, retreat- for Constans, in spring 344, marched over the Pyrenees. He quickly moved into Gaul, meeting at the battle of Turonum in February 345. Constantius expected to win- Constans himself did not lead his own armies, and was widely known to be an effeminate catamite.
Constantius did not expect the betrayal of his son-in-law, who had remained on the Rhine frontier in order to prevent Burgundian and Allemannic incursions into Gaul. This son-in-law, Chrodegang, would agree to come south, presumably to fight alongside Constantius, who appreciated the reinforcements.
The Battle of Turonum, however, is known best for its result- the treachery of Chrodegang and the other Germanic troops in exchange for land. Chrodegang had brought with him not just Salian warriors but the Salian people as well, and had been promised a reward of land for his people. Constantius was, according to some accounts, planning to renege on the land deal. More accounts, and popular history, say that Chrodegang was bribed by Constans. Chrodegang's treachery doomed Constantius, who is said to have been slain by his son-in-law in battle.
The faction of Constantius collapsed, as Constantine pressed north from Rome in spring 345. Constantine, however, would not live to meet Constans in battle. He was hit with a sudden fever in April 345- and he would die in Florentia only 10 days after contracting the illness. His forces remained together out of entropy, uniting around his infant son, whose name has been forgotten due to the damnatio memoriae enacted by Constans.
Constans, upon hearing of his other brother's death, would split his forces. Chrodegang would take his soldiers into Illyria and Pannonia, while Constans would march south. The civil war would end in November, with Constans triumphal entrance into Rome alongside his men and African grain. Constantius' sole son would disappear, smothered by a nurse for a few solidii. Chrodegang was given land across the Danube, controlling much of Pannonia, while Constans ruled the re-united but ravaged Western empire.
Constans was now undisputed Emperor of Rome in the west. He avoided war with Crispus, cautiously and intelligently avoiding a fight with a brother who, from all reports, was handily beating Shapur and whose forces had driven the Goths back over the Danube. Crispus had some designs on re-taking Illyria, but the possibility of Mesopotamia was a far greater prize.
Constans, at the time, faced the daunting prospect of recovering Imperial manpower and authority after the civil war. In particular, Britannia was vulnerable, to raids by Gaelic and Germanic pirates, and to raids from the tribal peoples of the north.
This being Constans, however, actual action was left to the small clique which had accompanied him to the blood-stained top of Roman society. His faction was the beginning of the slow German ascendance among the Roman elite. Constans' favorites, those who made up his guard and many of his companions, were largely Germans or half-Germans. Many of these favorites were involved with Constans sexually- as Church writing and popular legend take it, Constans was dominated by these Germans as an effeminate catamite, whose successes could be owed solely to his lieutenants. Constans would fight with the Church from the beginning of his reign- his not-quite-closeted approach to his homosexuality, his use of old pagan rituals alongside Christian worship, and his lukewarm faith did nothing to warm the Church fathers to him.
He was also on the outside of the remainder of the Roman military elite, many of whom had stayed "neutral" or who had jumped ship as Constantius and Constantine's efforts collapsed around them. Although Constans commanded the loyalty of men like his Caesar, Constantius Gallus, Magnentius and the pagan Julian- out of inertia as much as anything else- his behavior and favoritism alienated other members of the military, many of whom commanded more loyalty among the troops than the Emperor did.
Among the domestic population, Constans' support base rested on inertia and the favor of both the Romanized Germans, the neutral Christians, and the pagans. The devout Christians were almost immediately alienated by Constans' lifestyle, and in any case had supported Constantine in the civil wars. The pagans were largely Roman- and many people wavered in between paganism and Christianity. They had initially supported Constantius, who was suspected to be a crypto-pagan himself. Unlike the Christians, however, they were alright with a basic level of toleration- and Constans' respect for centuries of pagan tradition within Imperial ritual didn't hurt. This toleration only incensed the passionate Nicene faction more- a faction which often coincided with the dissatisfied parts of the military...
The cracks in Constans' realm were already, even upon his victory, beginning to show...
The Schism
The Council of Nicaea in 325 had been an attempt by Constantine I to bridge the divide between the Nicene and Arian factions. The council was contentious from the start- the Egyptian delegation was divided in narrow favor of the Arians, the African delegation was divided narrowly in favor of the faction that would come to be called Nicene, and the rest of the bishops were divided on largely geographical lines. The East was Arian, and the West was Nicene. This is not to say there weren't Nicenes in the East and Arians in the West, but the Church hierarchy was largely divided on those lines.
Fighting in the council itself, between the supporters of Arius and the Nicene faction, would lead Arius and his supporters to leave the council entirely in protest. The Nicene Creed, which declared Christ to be co-eternal with God the Father, was passed soon afterwards. However, the great controversy over its passage would lead Constantine to remain neutral in the dispute- the Roman Empire was neither Nicene or Arian until his death, when it was split between his sons.
Crispus, emperor of the East, is portrayed as a saint and as a zealot. However, modern scholars, looking into his youthful dabblings with the sun cult and with Manichaeism, largely conclude that his Arian devotion was a calculated political move to shore up his support in the East. If that was the case, it worked very well- under Crispus, Nicenes from Egypt to Macedonia fled as a result of official persecutions and high taxes. Many of the Egyptians would settle in the hills near Olissipona, founding the University of Olissipona in the outskirts of the city. Conversely, some Arians fled the West, although Constans, aloof as his father was, remained Nicene in name and word rather than in deed.
In the East, Crispus, in coalition with Arian Patriarch of Constantinople Nicholas "Thaumaturgos" of Myra, worked to entrench Arianism, and to continue to flesh out the tenets of their side of the schism. Although Arianism would not be officially complete theologically until the Council of Constantinople in 400, the doctrines adopted there had their start in the 340s and 350s.
The central doctrine of Arianism stood in defiance of the Nicene Creed: Jesus Christ was created at some point in time, and was therefore not co-eternal or co-substantial with God. God only became the father upon Jesus' birth into the world, and Jesus only became the Son upon his birth, before then existing as God's creation. Only God is uncreated. Furthermore, Arius had preached that the Holy Ghost, rather than being a person, was instead the force of God and his holiness on Earth, through Christ, the angels, the prophets and the miracles of saints. The Holy Spirit would generally be referred to as the Force in other languages.
The success of Arianism in the East produced the schism immediately- a trinitarian Church could not theologically co-exist with a Church focused on non-trinitarianism and Christ's subordinate role to the more important God the Father. Nicene Christianity said Mary was mother of God- in Arianism, Mary was Christotokos, the bearer of Christ. In Nicene Christianity, Christ was cosubstantial and coeternal with God- in Arian Christianity, he was neither. The actual mutual excommunications, and therefore the official schism, would not take place until 395-400, when new Church councils declared the anathematization of the other side.
This lack of official schism, and the fluid nature of the two Romes at the time, led to a continuation of intellectual exchange even as the two sides ossified theologically. The exchange largely took place in Greek. Despite the retroactive application of later linguistic divisions to the beginning of the Schism, both Churches largely spoke of theological terms in Greek, and wrote in that language. It would only be after the schism that the Western church wholly but slowly shifted to Latin services, with Greek being relegated to an ever decreasing role in theological texts over time. This exchange would lead to the next great theological division between the two branches- the debate over free will.