The massive megastructure built for eternity and still standing 1,700 years later

By Justin Calderon, CNN

Anuradhapura, Sri Lanka (CNN) — Visit the ancient city of Anuradhapura on a full moon day and the past feels anything but distant.

Buddhist pilgrims dressed in white walk barefoot along dusty paths. Saffron-robed monks chant at dawn. Foreign visitors — from Taiwan to Canada — join local worshipers in rituals that have been performed here, largely uninterrupted, for more than 2,000 years.

Set on Sri Lanka’s north-central plains, Anuradhapura was the island’s first great capital. Today, it remains one of the most sacred cities in the Buddhist world, known as the first place to adopt Buddhism outside of India. Scattered across its vast archaeological park are monasteries, reservoirs and stupas that rank among the most ambitious religious monuments ever built.

Towering above them is the immense, bubble-shaped dome of Jetavanaramaya — a structure so large that when it was completed in the early fourth century CE, it ranked as the third-largest man‑made building on Earth, surpassed only by the Great Pyramids of Giza.

Completed around 301 CE using an estimated 93.3 million baked mud bricks, the stupa originally rose to around 122 meters (400 feet), making it one of the tallest structures of the ancient world.

Today, after centuries of collapse, abandonment and restoration, Jetavanaramaya stands at roughly 71 meters (233 feet) — still monumental, but little more than half its original height. Even so, it remains the largest brick structure by volume ever constructed.

So vast is its mass that archaeologists estimate its bricks could build a three-foot-high wall stretching from London to Edinburgh — or from New York City to Pittsburgh.

Yet outside Sri Lanka, Jetavanaramaya is little known. Unlike the pyramids, it was not continuously visible to history. Jungle growth, shifting religious priorities and selective preservation gradually buried both the monument and much of its story, leaving one of the ancient world’s greatest engineering achievements largely forgotten.

Lost — and rediscovered

Jetavanaramaya refers not only to the stupa itself, but to the heart of a vast monastic complex known as Jetavana Vihara, designed to house hundreds of monks. Every structure in the complex was oriented toward the stupa, ensuring that monks stepping outside their residences would face it first — a daily reminder of devotion and cosmological order.

“About 200 monks lived here,” explains Godamune Pannaseeha, a bespectacled monk and senior archaeology officer in Anuradhapura, and one of the foremost contemporary experts on Jetavanaramaya.

“People came to offer robes, books, food — everything — to gain merit,” he says, pointing to the lower terraces of the stupa where offerings were once made, while walking a slow, clockwise circuit around its base. “This was a living religious city.”

From the outset, however, Jetavanaramaya was controversial. It was built on land traditionally associated with the Maha Vihara, the orthodox Theravada Buddhist establishment, reportedly without the consent of its monks. The complex later became associated with the Sagalika sect, which followed Mahayana‑leaning doctrines.

No Mahayana chronicles from ancient Sri Lanka have survived. Today, Sri Lanka remains a predominantly Theravada Buddhist nation. As a result, much of Jetavanaramaya’s history — including the political and doctrinal tensions surrounding its creation — must be reconstructed indirectly, leaving historians with incomplete and sometimes contested versions.

Ancient engineering at an immense scale

The technical challenges involved in building Jetavanaramaya were immense. Unlike Egypt’s stone pyramids, this colossal structure was built almost entirely from mud bricks — a material far more vulnerable to erosion and collapse.

“To replace one stone block, you need perhaps 10 bricks,” says Anura Manatunga, senior professor of archaeology at Sri Lanka’s University of Kelaniya. “That means millions upon millions of bricks had to be prepared, transported and laid with precision.”

Archaeologists have identified ancient brick kilns in and around Anuradhapura, confirming large‑scale brick production in the region. None, however, can yet be definitively linked to Jetavanaramaya or securely dated to the early fourth century.

Moving this volume of material would have required extraordinary organization — and labor. Here, the historical record is less clear. Some sources suggest the work relied on voluntary labor, while others indicate that enslaved people were also used.

According to Pannaseeha, ancient texts suggest that King Mahasena, who commissioned the stupa, supplemented local labour with captives taken during military campaigns in India.

“People brought into slavery were used to work on the stupa, as well as devotees and lay people,” he says.

While no records specifically mention animals at Jetavanaramaya, historians believe elephants and bullock carts were almost certainly used, as they were at other major Sri Lankan construction sites — including Ruwanwelisaya, the city’s most sacred stupa, built centuries earlier in 140 BCE.

Elephants likely hauled bricks and stamped down soil at the foundations, a technique used in traditional construction on the island until relatively recent times.

Scaffolding would have relied heavily on bamboo, bound with coir rope made from coconut fibre and jungle creepers. Metal was used sparingly, reserved for tools rather than structural elements.

Built to endure

Jetavanaramaya reflects the height of ancient Sri Lankan engineering knowledge. Its massive hemispherical form distributes weight efficiently, while its foundations were carefully prepared. Ancient chronicles describe how builders flooded excavated ground to observe absorption — a rudimentary but effective form of soil testing.

A fallen section of the stupa reveals further ingenuity. Pannaseeha points out a hollow, cylindrical chamber within the ruins that suggests an early understanding of ventilation.

Despite this sophistication, time has taken its toll. Earthquakes, monsoon rains and centuries of abandonment caused sections of the stupa to collapse. The last major renovation took place in the 12th century, during the reign of King Parakramabahu I.

More recent restoration efforts introduced cement into some outer layers — a decision archaeologists now believe may have accelerated deterioration rather than prevented it. The original mortar used to lay its bricks was composed of a mixture of finely crushed dolomite, limestone, sieved sand and clay.

Excavations have also uncovered reliquary caskets embedded throughout the stupa at different structural levels. These held sacred relics and ritual deposits, reinforcing Jetavanaramaya’s role not only as an architectural feat but as a sacred structure built from the inside out.

Among the most significant discoveries linked to Jetavanaramaya are gold panels depicting Bodhisattva imagery and inscribed with sections of the Prajñāpāramitā sutra, a foundational Mahayana Buddhist text. Now held at the National Museum in Colombo, the panels were written in Sanskrit using ancient local scripts.

They offer rare material evidence of Mahayana practice in ancient Sri Lanka, suggesting Jetavana was once a center of cosmopolitan Buddhist thought, connected by doctrine and trade routes to India and beyond.

A pinnacle of mystery

Standing at the base of the stupa, Pannaseeha gestures toward the damaged spire.

“Historical accounts say that a diamond once crowned the pinnacle, possibly to deflect lightning during monsoon storms,” he says.

The spire itself is unusual. “It resembles a tower,” he notes — a form some scholars believe may reflect technological influence from the Roman or broader Mediterranean world, transmitted through Indian Ocean trade networks.

Whether symbolic or functional, much about its construction remains unclear.

“We can see small remains of the decorative motifs, including those of the Naga, a cobra-hood form,” Pannaseeha adds, pointing to intricate carvings at the base. “But we still don’t know exactly how they were fixed in place.”

Grandeur and devotion

Jetavanaramaya’s immense scale invites comparison with Ruwanwelisaya, the gleaming white stupa nearby that today holds far greater religious significance for Sri Lankans.

Ruwanwelisaya is believed to enshrine some of Buddhism’s most venerated relics, including a portion of the Buddha’s remains. It remains the focal point of pilgrimage and national religious life.

Though smaller than Jetavanaramaya in its original form, Ruwanwelisaya has been continuously maintained and today rises higher than Jetavana’s truncated structure, standing at more than 100 meters (328 feet).

Where Jetavanaramaya represents architectural audacity and doctrinal debate, Ruwanwelisaya embodies devotional continuity.

Eetalawetunwawe Gnanathilaka Thero, one of the country’s most respected religious figures and chief monk at the Ruwanwelisaya, has noticed a steady increase in foreign visitors to Anuradhapura in recent years.

“First there was civil war, then a pandemic,” he says. “But the past two years, there has been a noticeable increase in foreign visitors to our holy city.”

Travelers are welcome to observe — and participate in — any of the nine daily puja rituals, with the first beginning at dawn.

Visit on a full moon day and thousands of pilgrims arrive, waiting patiently to enter Ruwanwelisaya and Sri Maha Bodhi, the temple that surrounds a sacred fig tree believed to be grown from a sapling of the tree under which the Buddha attained enlightenment.

Last of its kind

Perhaps the most striking fact about Jetavanaramaya is that nothing like it was ever built again. For nearly 700 years after its completion, no stupa of comparable scale was attempted in Sri Lanka.

“This was the last truly gigantic stupa,” Manatunga says. “Not only here, but even in Southeast Asia, later builders adopted the same bubble-shaped form — but never at this scale.”

Jetavanaramaya stands today as evidence of an ancient society capable of organizing labor, materials and engineering knowledge on a scale that rivalled any civilization of its time.

That it remains relatively unknown beyond Sri Lanka may be one of history’s great oversights — a reminder that some of the ancient world’s most extraordinary achievements were not carved in stone, but shaped from earth, devotion and human ingenuity.

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