Scholars estimate that between 90 and 99 percent of all ancient Greek and Roman literature has been lost. The writings of ancient atheists and religious skeptics, then, stood little chance of surviving. Given that accusations of impiety could cost a person their freedom—or even their life—it is hardly surprising that such works were among the first to be consigned to the flames.
This makes it all the more remarkable that so many heretical writings and fragments have nevertheless survived, suggesting that religious skepticism—and perhaps even outright atheism—was far more widespread in the ancient world than is commonly assumed. The following Ancient Atheism Learning Path—developed over the past several years by scrutinizing the surviving works of religious dissent in ancient Greece and Rome—aims to demonstrate precisely that.
Beginning in the sixth century BCE with Xenophanes and ending with the last pagan emperor of the Roman Empire, this learning path introduces the thinkers who first dared to challenge divine authority long before the rise of the European Enlightenment. Across thirteen original essays, you’ll discover how these ancient critics anticipated modern debates about science, morality, religion, and human freedom—ideas that would eventually help humanity emerge from the Age of Faith.
In this learning path, you’ll discover:
- Why atheism and religious skepticism are far older than most people realize.
- The philosophers who first challenged divine authority.
- How ancient thinkers anticipated modern science, secular ethics, biblical criticism, and the psychology of religion.
- Why many atheist writings have disappeared from history.
- The intellectual tools that remain useful for evaluating religious claims today.
Note: Throughout this course, atheism is understood in its broader historical sense to include the rejection of the gods of orthodox religion, even when it did not entail the denial of every conceivable deity. Thinkers who criticized traditional religion while affirming an impersonal divine principle or non-interventionist gods are therefore included as important precursors to the explicit atheism that emerged in later centuries.
Every essay in this collection is freely available without a subscription and without advertising. If you find this work valuable, please consider supporting the site with a donation. Every contribution goes directly toward the (AI-free) research, writing, and development of future essays and learning paths.
Lesson 1: The First Heretic: Xenophanes and the Birth of Religious Skepticism (c. 570–478 BCE)
Discover how Xenophanes of Colophon became one of the first thinkers in history to challenge traditional religion by questioning the nature and origins of the gods. You’ll learn how Xenophanes replaced supernatural explanations of nature with rational inquiry, argued that humans create gods in their own image, and exposed how religious beliefs often reflect the cultures that produce them. This article traces his revolutionary ideas about anthropomorphism, morality, and natural philosophy, showing how his skepticism helped lay the foundation for later atheism, science, and secular thought—even though he stopped short of rejecting all belief in the divine.
Lesson 2: Piety on Trial: Socrates and the Downfall of Divine Command Theory (c. 470–399 BCE)
If right and wrong are determined by God’s commands, is morality anything more than obedience? In this article, you’ll explore Socrates’ famous confrontation with Euthyphro and the dilemma that has challenged religious morality for more than 2,400 years. You’ll learn why the Euthyphro dilemma undermines divine command theory, how Socrates argued that moral truths must exist independently of the gods, and why this dialogue became one of the foundational texts of secular ethics.
Lesson 3: The First Atheist: Diagoras of Melos and the Psychology of Superstition (c. 465–410 BCE)
In this article, you’ll learn why Diagoras of Melos earned a reputation as the ancient world’s first atheist and how his skepticism emerged from a powerful observation about human psychology. By examining the stories surrounding Diagoras and his critiques of Greek religion, this article explores why people are often drawn to superstition, why they mistake coincidence for divine intervention, and why religious beliefs can persist even in the face of contradictory evidence.
Lesson 4: On the Sacred Disease: How Hippocrates Exposed the Fallacy of Faith Healing (c. 460–370 BCE )
Discover how Hippocrates transformed medicine by rejecting supernatural explanations for disease and insisting that illness has natural causes that can be understood through observation and reason. This article explores his groundbreaking critique of faith healing, exorcisms, and medical charlatanism, showing how On the Sacred Disease helped lay the foundations of scientific medicine while exposing a pattern of pseudoscience that continues to this day.
Lesson 5: Footnotes to Democritus: The Ancient Roots of Materialism and Secular Humanism (c. 460–370 BCE)
This article explores why the ancient Greek philosopher Democritus deserves to be remembered not merely as the father of atomism, but as one of the earliest architects of a thoroughly naturalistic worldview. You’ll learn how his materialist philosophy anticipated many of the core assumptions of modern science, rejected supernatural explanations in favor of natural causes, and laid the intellectual foundations for secular humanism centuries before the Enlightenment. You’ll also learn that history’s overwhelming admiration for Plato came at the expense of Democritus, and how Western civilization might have developed differently had Democritus’ naturalistic approach become the dominant tradition.
Lesson 6: Return to Eden: Epicurus and the Pursuit of Happiness Without Religion (341–270 BCE)
This article explores how Epicurus transformed religious skepticism into a complete philosophy of life built on reason rather than faith. You’ll learn why he believed that fear of the gods and fear of death are the greatest obstacles to human happiness, how his materialist philosophy dismantled the need for an afterlife, and why his vision of pleasure had little to do with indulgence and everything to do with tranquility, friendship, and freedom from anxiety. By overturning the biblical story of Eden, Epicurus offers a compelling secular alternative to religion—arguing that paradise is not something we regain after death, but something we can create for ourselves in this life.
Lesson 7: A World Full of Gods: Cicero and the Limits of Human Knowledge (106–43 BCE)
This article explores why some of humanity’s biggest questions—about God, consciousness, and the ultimate nature of reality—may lie beyond the limits of human understanding. Drawing on the ideas of Noam Chomsky and the Roman philosopher Cicero, it argues that intellectual humility is often a wiser response than dogmatic certainty, especially in matters of religion. Along the way, you’ll discover why science succeeds where theology is so often divisive, why skepticism can be a virtue rather than a weakness, and why admitting “I don’t know” may be the most rational position of all.
Lesson 8: The Stoic Alternative to Religion: Six Principles for Handling Adversity Without God (c. 50–135 CE)
Explore how Stoicism provides a practical, secular alternative to religion for coping with life’s greatest hardships. Drawing on the teachings of Epictetus and Marcus Aurelius, you’ll learn six timeless principles for overcoming fear, anxiety, anger, setbacks, loss, and envy by focusing on what lies within your control: your character. Rather than relying on divine intervention or supernatural consolation, Stoicism offers a disciplined approach to building resilience, inner tranquility, and moral strength through reason, self-mastery, and the acceptance of reality as it is.
Lesson 9: The Fall of Olympus: How Lucian Exposed the Absurdity of the Gods (c. 125–180 CE)
In this article, you’ll discover how the second-century satirist Lucian of Samosata used relentless cross-examination to dismantle the authority of the Olympian gods. Through his brilliant dialogue between Zeus and the philosopher Cyniscus, Lucian exposes the contradictions at the heart of Greek religion—showing that if Fate determines every event, then prayer, sacrifice, and divine justice become meaningless. Lucian’s satire is a powerful philosophical critique of religious belief, revealing how reason and ridicule can succeed where direct argument often fails, and why his insights remain relevant to modern discussions about faith and skepticism.
Lesson 10: Unoriginal Sin: Celsus on the Borrowed Origins of the Christian Faith (c. 175–180 CE)
In this article, you’ll learn how the second-century philosopher Celsus challenged the origins and claims of Christianity in his work The True Word. You’ll explore Celsus’s argument that Christianity was not a divinely revealed truth but a faith built from borrowed ideas, reshaped myths, and traditions inherited from older cultures. You will also learn how early Christian teachers targeted the uneducated, and how stories of miracles, resurrections, and virgin births were a dime a dozen in the ancient world.
Lesson 11: The Skeptic’s Guide to Religion: Sextus Empiricus and the Art of Withholding Judgment (c. 180–210 CE)
Discover how Sextus Empiricus and the skeptical tradition challenged religious certainty by practicing the art of withholding judgment. Rather than arguing that the gods do not exist, Sextus exposed the limits of human knowledge and showed how competing beliefs, contradictory religious claims, and unreliable perceptions make dogmatic conclusions impossible to justify. You’ll also learn how ancient skepticism became a powerful tool for questioning religious authority and defending the freedom to think independently.
Lesson 12: Testing the New Testament: Porphyry and the Origin of Biblical Criticism (c. 234–305 CE)
In this article, you’ll learn how Porphyry became one of Christianity’s earliest and most formidable critics by subjecting the New Testament to rigorous historical and textual analysis. You’ll learn how Porphyry examined scripture for contradictions, questioned the authorship and dating of biblical books, and challenged the fulfillment of prophecy. This article explores how his methods anticipated many principles of modern biblical criticism, demonstrating that the historical investigation of sacred texts began centuries before the Enlightenment. It also examines the Church’s determined efforts to suppress his writings, underscoring the enduring tension between religious authority and free inquiry.
Lesson 13: Against the Galileans: Julian on the Contradiction at the Heart of Scripture (331–363 CE)
Discover how Julian the Apostate launched one of antiquity’s most sophisticated critiques of Christianity by exposing what he saw as contradictions at the heart of scripture. Drawing on his deep knowledge of both the Bible and classical philosophy, Julian argued that Christian theology was internally inconsistent, that its interpretation of the Hebrew Scriptures was flawed, and that many of its central doctrines lacked rational and historical support. The article explores how Against the Galileans challenged Christianity on its own textual foundations and illustrates why Julian’s arguments remain an important milestone in the history of religious criticism and the defense of reason over dogma.
Up Next
Ancient skepticism did not disappear with the fall of Rome. Though many classical works were lost or forgotten, their ideas survived and reemerged during the Renaissance and early modern period in the writings of thinkers such as Giordano Bruno, Galileo Galilei, Francis Bacon, Thomas Hobbes, Baruch Spinoza, and Pierre Bayle. Continue to Atheism in the Seventeenth Century (In Development).