As the religious as well as the political leader of the Roman Empire, Constantine inevitably had to deal with matters of heresy. Heresy had not been a problem for the older Roman religions, which left their devotees much freer in their selection of cults and rites than Christians would, or could, ever be. But Christianity was an intolerant religion which placed extreme emphasis on orthodoxy of belief. More and more, bristling phalanxes of bishops and theologians stood ready to do battle over the smallest inflection, the least quillet of doctrinal meaning. The result was a nightmare of religio-political correctness, in which the stakes were not simply the tolerance or disapproval of others but (it was believed) the soul’s prospect of eternity in Hell. This gave a terrible seriousness to theological argument. Ridiculous as many such debates may seem from a twenty-first-century viewpoint (there can be few believers left who care how many angels can dance on the head of a pin), in the fourth century they gave rise to the first Christian persecutions, in which one wing of the faithful tormented and killed members of another over what now look like absurdly minuscule differences of belief.
The first such split was over “Donatism.” This heresy had caused a schism in the Church in Africa, which had only slight repercussions in Europe. It arose, quite simply, from the fact that during the persecutions by Diocletian some Christians had knuckled under, denying their faith to save their skins. Now that Diocletian was gone and Christianity had become the state religion, these quislings sought to rejoin the Church and be forgiven. But a strong group opposed this, tooth and nail. To them, there must be no future forgiveness for former collaborators. Their leader was a Carthaginian priest named Donatus. This, one might have thought, could have been resolved at the lower levels of the Church, but it proved insoluble. The emperor himself had to rule on it—and he did, ordering the army to force the Donatists into submission. Thus began the first orthodox, official Christian persecution and martyrdom of “heretic” Christians.
There would be others. The most spectacular, bitter, and bloody of them was the fourth-century Arian persecution, which split the Church down the middle and caused seemingly illimitable suffering to many as Christians rejected, tormented, and frequently slaughtered one another over a single vowel, an extra “o,” descriptive of Christ’s relationship to God the Father and the Holy Spirit. Was Christ homoousios with God the Father (made of the same essence as God, and existing from the beginning of time), or merely homousios (similar in essence but not the same, and created after the Father, there having been “a time when he was not”)? This seemingly absurd dispute originated in Alexandria, with a highly intellectual priest named Arius (d. 336), who fiercely objected to any prevalent reading of the Scriptures that claimed that Christ was the Son of God, “begotten, not made,” sharing the Father’s divine essence, and existing for all time. Orthodox Christianity disagreed. It regarded the dogma of the Trinity—God consisting of three persons, the Father, Son, and Holy Ghost, who form one substance—as a basic and central tenet of faith, which it was heresy to deny. It was this “one substance” clause, as it were, that generated the passion over whether Christ was homoousios or homousios with his Father. The dogma of the Trinity was a “mystery,” not comprehensible through human logic; there were later attempts to rationalize it, though, as when a Victorian cleric argued that one need only imagine a carriage with three persons riding in it—to which another Victorian cleric retorted that one should try instead to envision three carriages with one single person riding in them.
The dispute was settled, after a fashion, when Constantine himself felt obliged to intervene. In 325, he summoned a council of bishops in the city of Nicaea to pronounce on the ideas of Arius. Their verdict, not unexpectedly, was that Arianism was a heresy to be stamped out. This was enshrined in the Nicene Creed, a document repudiating Arius and agreed to, pro forma, by all the bishops of the Catholic Church. Jesus was now officially homoousios with his father.
Despite Constantine’s gestures toward relative tolerance, by 325 paganism was a lost cause within the Roman Empire. Many of the supporters of Constantine’s erstwhile co-emperor Licinius, still a pagan, were killed off after his death. (Constantine was said to have had Licinius himself strangled, though the circumstances remain murky.) Most of the survivors were dismissed. Pagan rituals, such as sacrifice to the gods, divination, or the consultation of oracles, were now banned absolutely. In effect—and luckily for the archaeology of the future—pagans could keep their shrines, temples, and sacred groves, not demolish them, but not worship in them. Constantine made sure that no more pagans, or even those who had recently abjured pagan beliefs, would be appointed as magistrates, prefects, or provincial governors. All preference would go to Christians. But active persecution of pagan religions was not required, since it might provoke violent counter-reactions. Constantine wanted peace, albeit peace only on terms of submission to Christianity.
Apart from Christianity itself, the great beneficiary of Constantine’s power was the city of Constantinople, which he founded in 330, not quite a quarter-century after he was proclaimed emperor. To say that Constantinople was in any real sense the “new Rome,” replacing the original by a single act of will, is of course a foolish simplification. But Constantine was determined to found a new and great Christian city where he and later Christian emperors could hold their court in an environment not contaminated by physical memories of paganism—no temples to the gods, no relics of pre-Christian institutions. This ruled out rebuilding the site of Troy, which he seems to have briefly considered for its mythological attractions, but then rejected because he did not want his actions attributed to Homeric inspiration.
On Europe’s most southeasterly peninsula, between the saltwater strait known as the Golden Horn and the inlet from the Sea of Marmara called the Bosporus, was a neck of land on which stood the remains of a Greek settlement and the beginnings of a minor Roman city, its origins in the seventh century B.C.E. This city was known as Byzantion. It had obvious strategic and trade advantages. It stood at the intersection of the land route from Europe to Asia and the sea route from the Mediterranean to the Black Sea. It was well placed for self-defense. Most of it was girdled by the waters of the Golden Horn to the north, and the Sea of Marmara to the south. It needed only a wall across its base, between the bodies of water, to make it very difficult to invade. The Via Egnatia linked it to Rome, and from it two other roads led east, toward Asia Minor. The land behind it was indulgent to crops and fruit, and rich in building stone. The sea around it fairly teemed with fish. Aqueducts gave it water, and as soon as serious building work began on the new city, they would be supplanted by many large cisterns, some forty of which survive (and are full of fresh water) to the present day—water palaces, one of which is known to the Turks as “the Cistern of a Thousand and One Columns,” which must be close to a factual description.