Editor’s Note: This essay is part of our extended series celebrating the 1,700th anniversary of the Nicene Creed.
Few roads have mattered more to the development of Christianity than the Via Militaris, a Roman military highway stretching nearly a thousand miles from Constantinople across the Balkans to Sirmium—modern-day Sremska Mitrovica in Serbia. Along this strategic corridor, where the Greek East faded into the Latin West, emperors marched, legions moved to guard the Danube frontier, and imperial officials carried messages and mandates between Rome’s twin capitals.
But in the fourth century, the Via Militaris served also as a theological highway. The Emperor Constantine himself was born in a city along its path, and in the decades following the Council of Nicaea in 325, no fewer than nine major church councils were held along this route, as bishops wrestled with the most urgent and divisive question of the age: the true nature of Jesus Christ.
At the heart of these disputes lay a single, potent word: homoousion—“of one substance with the Father.” This term, enshrined in the Nicene Creed, became the dividing line in a dispute that would stretch across more than a century, reshaping not only the Church but also the very structures of thought in Western civilization.
It wasn’t only their theological conclusions that would echo across generations, but the process of argument—the deep engagement with Scripture, tradition, reason, and philosophy that forged a new way of thinking. These controversies, at once doctrinal and political, intimate and imperial, taught the world that ideas matter and that how we argue about them matters even more.
The Birth of a Crisis
The story begins not with a council, but with a priest: Arius of Alexandria. Trained in the philosophical traditions of his day and shaped by a deep concern for the uniqueness of God the Father, Arius preached that the Son, while exalted, was not eternal. His fiercest opponents accused him of teaching this: “There was when he was not.”
To many others, especially bishops in the East, Arius’s teaching seemed like a logical compromise. After all, begotten implied some form of origin, and Scripture at times spoke of Christ’s obedience and submission. But to others, including Bishop Alexander of Alexandria and his eventual successor Athanasius, this teaching undermined the very foundation of Christian salvation. If Christ were not fully divine, how could he redeem humanity? If he were not eternal, could he truly mediate between God and creation?
The disagreement escalated quickly. Letters flew, tempers flared, and before long the Emperor was drawn into the fray. Constantine, newly victorious and eager to unify his freshly Christianizing empire, called for a council to settle the matter. Nicaea was chosen as the site, and in late spring of 325 bishops from across the known world (though primarily from the East) gathered there to deliberate.
The result was a bold and enduring statement: the Nicene Creed. Christ was not simply like the Father (homoiousios), he was homoousios, of the same substance. He was, as the Creed affirms, “God from God, Light from Light, true God from true God.”
But the Creed, while decisive, was far from universally welcomed. Some objected to the use of non-scriptural language. Others feared that homoousios could be interpreted as implying a blurring of the persons of the Trinity—a throwback to the heresy of Sabellianism. And as Constantine’s successors took the throne, imperial support for the Nicene formula waxed and waned. Councils were convened and reconvened, often under duress. Bishops were exiled, reinstated, and exiled again. Theological lines hardened and fractured.
To some modern observers, this era can look like a chaotic power struggle wrapped in theological garb. But beneath the political maneuvering lay a more profound development: the birth of a culture in which doctrine was not merely academic. The very fabric of the Christian life was seen to rest on precise truths about who Christ is.
When Doctrine Goes Public
What made the Nicene controversies so groundbreaking was not only their content but their context. In the ancient world, intellectual debates were typically the province of elites. Greek philosophers debated metaphysics in schools and symposia, but rarely did such disputes spill into the public square or capture the attention of rulers.
By contrast, the fourth-century Church brought doctrinal argument into the heart of society. These weren’t abstract musings confined to theologians and monks. They were matters of public concern. Emperors convened councils, cities erupted in riots, bishops were driven into exile by mobs or were summoned by imperial guards.
In North Africa, Egypt, and Asia Minor, theological factions divided communities. Imperial officials found themselves struggling to mediate between rival ecclesial groups as they tried to govern ideologically divided societies. Doctrinal disputes fueled not only sermons and treatises, but also street protests and imperial edicts. Famously, Arius’s own teaching were sung in taverns. Few found it easy to be neutral.
And why? It’s because these disputes were not really about hair-splitting metaphysical definitions, but rather about the core of Christian existence. The debates about Christ’s two natures were, at bottom, debates about what it means to be human. And the answer to that question had consequences beyond Christology, touching as it did on every aspect of being a human being in a world created by God and a society that ought (as all believed) to be ordered toward the good life.
The intensity of the Nicene disputes was something the classical world had never seen. There had been other mass religious movements, of course, and other philosophical schools. But never before had abstract ideas about God and personhood created such social upheaval. Christianity had introduced something new: a faith that demanded not just personal belief, but public confession and doctrinal clarity.
A New Kind of Thinking
The theologians of the fourth and fifth centuries didn’t simply assert dogma. They reasoned. They argued. They drew on Scripture, but also on the tools of classical education: logic, rhetoric, and philosophy. The result was a new kind of theological inquiry that honored the mystery of God while striving for intellectual rigor.
Figures like Athanasius, the Cappadocian Fathers, Augustine of Hippo, and Cyril of Alexandria engaged not just in theology, but in anthropology, epistemology, and political theory. In defending the divinity and humanity of Christ, they explored the very boundaries of what it means to be a person. They wrestled with questions of freedom, will, politics, and social relationships—questions that would lay the groundwork for centuries of Christian and even secular thought.
In the process, they shaped the intellectual architecture of the West. The idea that truth is worth pursuing, even at great personal cost; that beliefs must be reasoned and articulated with care; that doctrine matters because reality matters—these are all the legacies of the Nicene controversies.
And as the Church articulated its faith, it also learned how to disagree. Slowly, painfully, and imperfectly, early Christians began to develop norms for theological dispute—conciliar processes, appeals to Scripture, consensus-building, and eventually creeds. It was not a linear or peaceful journey. But by the time of the Council of Chalcedon in 451, the Church had hammered out not only a Christological definition, but also a method of deliberation that would sustain its doctrinal integrity for centuries.
Ideas Matter: Then and Now
Nearly 1,700 years later, the echoes of these early controversies remain with us. We live in a world that still experiences the power—and peril—of ideas. From political ideologies to social movements, we have inherited a landscape in which belief shapes culture, identity, and law.
But unlike the early Church, we’re not inventing this from scratch. We have institutions, traditions, and models that help us navigate disagreement. We know (or ought to know) that truth cannot be imposed by fiat, nor reduced to majority vote. We have learned—often painfully—that unity and clarity require conviction, patience, and love.
In a time when theological disagreements often devolve into tribalism or apathy, the Nicene legacy reminds us that the pursuit of truth is holy work. The bishops and theologians of the fourth and fifth centuries didn’t always get it right, and they certainly didn’t always treat one another charitably. But they cared deeply about the faith “once delivered to the saints.” They understood that who Christ shapes how we understand ourselves, our world, and our place within it.
Like the Via Militaris, the road from Nicaea was long, bridging worlds and cultures. Yet its destination was not a perilous frontier, but a transformed world shaped by the enduring belief that ideas matter, that truth is worth pursuing, and that in Christ, the eternal Word, truth has been revealed for all humankind.
The Rev. Mark Clavier, PhD is Canon Theologian of the Diocese of Swansea and Brecon in the Church in Wales, Bishop's Chaplain, and Vicar of St Mary's Brecon. He is the author of five books including Eloquent Wisdom: Rhetoric, Cosmology, and Delight in the Theology of Augustine of Hippo. Previous appointments include Vice Principal of St. Stephen's House, Oxford, Dean of St. Michael's Theological College, Llandaff, and parish ministry in the US and the UK.
