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15 Forgotten Religions That Once Had Millions of Followers

Shannon Quinn - June 30, 2025

Throughout history, religions have risen and fallen, leaving lasting marks on societies and cultures around the globe. Vast empires and bustling cities once pulsed with devotion to faiths that, today, are nearly forgotten. These belief systems shaped laws, inspired art, and influenced daily life for millions. Yet over centuries, many faded from memory—overshadowed by newer traditions or lost to the tides of time. This article explores fifteen remarkable religions that once commanded millions of followers, but are now relics of our collective past.

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1. Manichaeism

Founded by the prophet Mani in the 3rd century CE, Manichaeism rapidly expanded from the heart of the Roman Empire all the way to China. This unique faith fused elements of Christianity, Zoroastrianism, and Buddhism, creating a religion centered on the cosmic struggle between light and darkness. At its height, Manichaeism attracted millions and even rivaled Christianity in influence. However, it was eventually labeled heretical and ruthlessly suppressed. Learn more from World History Encyclopedia.

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2. Mithraism

Mithraism thrived within the Roman Empire, especially among soldiers from the 1st to 4th centuries CE. Centered on the worship of the god Mithras, followers participated in mysterious rituals conducted in underground temples known as Mithraea. Its secretive nature and exclusive membership made it influential across the empire. However, as Christianity rose to prominence, Mithraism quickly declined and was eventually forgotten. History.com on Mithraism

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3. Zoroastrianism (Ancient Persian Variant)

Once the official faith of the powerful Persian empires, ancient Zoroastrianism profoundly influenced later religious ideas about good, evil, and the afterlife. Its teachings emphasized the eternal struggle between the benevolent Ahura Mazda and the evil Angra Mainyu. Millions once followed its sacred fire rituals and moral codes. Although a small Zoroastrian community still exists, the original expansive religion has largely faded from prominence. Britannica on Zoroastrianism

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4. Tengriism

Tengriism was the spiritual backbone of Turkic and Mongolic peoples across the vast steppes of Central Asia. Centered on the sky god Tengri, it shaped the worldviews and governance of mighty empires such as the Mongols. Over centuries, Tengriism’s influence waned as Islam and Buddhism spread throughout the region, leading to its decline. Oxford Reference on Tengriism

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5. Ancient Egyptian Religion

For thousands of years, Ancient Egyptians honored a complex pantheon featuring deities such as Ra, Osiris, and Isis. Their faith inspired elaborate rituals and awe-inspiring monuments like the pyramids and massive temples. Religion touched every aspect of life, from daily routines to royal ceremonies and burial customs. However, after the Roman conquest and the spread of Christianity, the ancient religion faded into history. Smithsonian Magazine on Ancient Egyptian Religion

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6. Orphism

Orphism was a Greek mystery religion that focused on the soul’s journey, reincarnation, and ultimate purification. Its teachings inspired later Greek philosophers and spread widely across the Mediterranean. As Christianity gained influence, Orphism gradually disappeared, leaving only traces in myth and philosophy. Theoi Greek Mythology on Orphism

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7. The Cult of Isis

Originating in Egypt, the Cult of Isis spread rapidly throughout the Roman Empire, captivating millions with its promises of salvation and eternal life. Magnificent temples dedicated to Isis could be found as far west as Britain and as far east as Persia. However, the rise of Christianity as the state religion led to the cult’s eventual decline. Ancient History Encyclopedia on Isis

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8. Mandaeism

Mandaeism once flourished in ancient Mesopotamia, centering its faith on reverence for John the Baptist and the importance of water rituals for spiritual purity. Its followers developed a rich tradition of ceremonies and sacred texts. Today, only a small community survives, preserving their unique beliefs against the odds. BBC Religion on Mandaeans

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9. Yazidism (Historic Reach)

Yazidism once claimed millions of adherents across the Middle East, with possible connections to ancient Mesopotamian religions. This unique faith blends elements from several ancient traditions and centers around the worship of Melek Taus, the Peacock Angel. Today, Yazidism endures in small, resilient communities in Iraq and Syria, striving to maintain their rich heritage. Encyclopedia Britannica on Yazidism

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10. Catharism

Catharism was a powerful Christian dualist movement that flourished in southern France and northern Italy between the 12th and 14th centuries. Adherents, called “Perfects,” rejected the authority of the Catholic Church and promoted a strict, ascetic lifestyle. The movement grew rapidly until it was brutally suppressed during the Albigensian Crusade. Though Catharism vanished, its ideals and stories continue to intrigue historians. History Today on Cathars

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11. Bon (Pre-Buddhist Tibetan Religion)

Bon was the original spiritual tradition of Tibet, marked by rituals devoted to mountain spirits, nature, and ancestor worship. While Buddhism eventually became dominant in Tibet, traces of Bon’s ancient practices still survive in some Himalayan areas. Its unique blend of animism and shamanism continues to fascinate scholars and spiritual seekers. Britannica on Bon

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12. Donatism

Donatism was a powerful Christian movement that arose in North Africa, splitting from mainstream Catholicism over fierce debates about purity and legitimate church leadership. At its peak, Donatism attracted millions of followers and created deep divisions. It was eventually suppressed through forceful actions by both Church and state authorities. Oxford Reference on Donatism

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13. Hellenistic Polytheism

Hellenistic polytheism was the classical Greek tradition of worshipping a diverse pantheon—from Zeus to Athena—permeating every aspect of personal and civic life across the Mediterranean. Rituals, festivals, and temples were woven into daily existence. As Christianity spread, this ancient system slowly faded, but its vibrant myths and stories still influence art, literature, and culture today. Encyclopedia Britannica on Greek Religion

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14. Arianism

Arianism was a prominent Christian movement from the 4th to 7th centuries, teaching that Jesus was not fully divine. This doctrine gained widespread support, especially among Germanic tribes, and posed a significant challenge to Catholic orthodoxy. After intense theological disputes, Arianism was ultimately declared heretical and gradually disappeared. Encyclopedia Britannica on Arianism

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15. Canaanite Religion

The ancient Canaanite religion flourished in the Levant, featuring a complex pantheon led by deities like Baal and Asherah. Its influence extended across the region, shaping the beliefs of neighboring cultures such as the Israelites and Phoenicians. Over centuries, conquest and cultural assimilation caused the Canaanite faith to vanish.Yet, echoes of its myths and rituals still linger in later traditions. World History Encyclopedia on Canaanite Religion

Many of these once-massive faiths are now mere shadows in history books, but their legacies live on. By remembering them, we gain insight into humanity’s enduring quest for meaning and connection. What other forgotten religions might have shaped the world as we know it?

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