Challenges the Colosseum Has Faced

The Colosseum we see today—partially collapsed, stripped of its outer marble, its interior gutted—looks nothing like the building that opened in 80 CE. That structure was ornate, and fully functional. What happened in the nearly two thousand years since wasn’t a single catastrophic event but a long accumulation of damage from earthquakes, fires, neglect, scavenging, repurposing, and the impacts of an urban city growing up around it.

The building has survived, but only barely, and most recently, only with substantial intervention and monitoring.

Historical Challenges

Earthquakes

Rome sits in a seismically active zone, and the Colosseum has been shaken repeatedly over the centuries. The most destructive earthquakes struck in 443, 801, 847, 1231 and 1349 CE.

The 443 quake caused massive damage to the arena floor and the seating tiers. This quake likely signaled the beginning of the end for the hypogeum, as the lifts became too expensive to maintain alongside the necessary major structural repairs.

The 847 quake damaged the outer wall, particularly on the southern side, causing sections of the arcade to crack and shift.

Another massive quake in 1231 caused the collapse of a significant portion of the southwest outerwall. The 1349 earthquake was far worse. It caused a major collapse of the exterior wall on the south side—the side facing away from the hill where the foundation was less stable due to the slope of the terrain. Large sections of the outer travertine façade fell away, leaving the gaping opening visible today.

These collapses weren’t repaired. By the 14th century, no one was using the Colosseum for its original purpose, and there was no political or financial incentive to restore a defunct entertainment venue. The fallen blocks of travertine were left where they lay or, more often, carried off for reuse elsewhere.

By the 1800s, the building was in such a precarious state that it threatened to vanish entirely. It wasn’t until the 19th century that the Papacy finally intervened to halt the “domino effect” of structural collapse triggered by centuries of seismic damage. If you look at the ends of the surviving outer ring today, you can see the result of this desperate triage: massive, triangular brick buttresses that lean against the ancient travertine like giant bookends, bracing the remaining arches against future tremors.

Decay of Wooden Components

The Colosseum wasn’t built entirely of stone. Key structural and functional elements were made of wood: the arena floor, the attic framework that supported the awning system, interior staircases, and much of the seating superstructure.

Wood rots, burns, and deteriorates when not maintained. Once the games ended in the 5th and 6th centuries, there was no reason to maintain these components. The arena floor—the wooden platform covered with sand that concealed the hypogeum—decayed and collapsed, exposing the underground chambers to the elements. The attic, which housed the mechanisms for the velarium (the retractable awning that shaded spectators), similarly deteriorated and eventually disappeared entirely.

Scavenging for Materials

For centuries after the Colosseum ceased operation, it was treated as a quarry. The building was full of valuable, already-cut stone and metal, and Rome’s later builders helped themselves.

The outer façade was clad in travertine limestone blocks, held together with iron clamps. Lead pipes ran through the building. Scavengers pried out the iron, leaving the pockmarked holes still visible across the surface today, and stripped the building of its pipes. Bronze fittings, lead piping, and other metal components were melted down. By the Renaissance, the Colosseum had been so thoroughly picked over that there was little left but the brick and concrete core.

The travertine itself was carted away to build churches, palaces, and other structures across Rome. The Palazzo Barberini, Palazzo Venezia, and St. Peter’s Basilica all contain stone taken from the Colosseum.

Repurposing and Neglect

For over a thousand years, no one was responsible for maintaining the Colosseum. Changes were made to the building to accommodate the many different purposes later generations found for the Colosseum, including during its time as a pivotal part of the 13th century “tower wars.”

Vegetation took root in the walls. Rain eroded exposed surfaces. Animals nested in the corridors. The hypogeum filled with debris and soil, becoming completely buried.

It wasn’t until the 18th and 19th centuries that the Colosseum began to be seen as a monument worth preserving rather than a resource to exploit. By then, the damage was irreversible.

Modern Challenges

Today, the monument faces a set of challenges that differ fundamentally from the earthquakes, fires, and neglect that damaged it in centuries past.

Climate Change and Flooding

The hypogeum, the two-level underground complex beneath the arena floor, was never designed to handle water. When it was built in the late first century, the drainage systems were intended to manage groundwater seepage and occasional rainwater. They were not built for the kind of extreme weather events that have become increasingly common in recent decades.

Flooding in the hypogeum is now a regular occurrence. Water levels routinely rise 1.5 meters above ground level during heavy rains, submerging the corridors and chambers. In 2011, an extraordinary storm flooded the entire underground area with sixteen million liters of water, reaching six meters in height.

Repeated flooding accelerates erosion of the brick and concrete walls, destabilizes the foundations of the arena floor above, and creates conditions for biological growth that can further damage ancient materials. The water also carries pollutants and salts that, when they dry, crystallize within the stone and cause it to crack and flake.

Climate change is also altering humidity levels across southern Europe. Lower humidity means more salt deposits on marble and limestone, which weakens the stone.

The Italian government has allocated significant funding to address these threats, including the construction of a new retractable arena floor designed in part to protect the hypogeum from water damage. The floor, scheduled for completion in the coming years, will incorporate advanced drainage systems and materials that can withstand both the flooding and the movement of visitors walking above.

Air Pollution

The Colosseum is located in the center of a modern city with millions of residents, heavy traffic, and industrial activity. Decades of exposure to urban air pollution have left a visible mark on the stone.

Pollutants in the air—particularly sulfur dioxide, nitrogen oxides, and particulate matter from vehicle exhaust—react with the calcium carbonate in the remaining travertine and marble to form gypsum, a brittle compound that weakens the stone’s surface. Over time, this leads to a phenomenon called “black crust,” where the surface of the stone darkens and begins to flake away.

The pollution doesn’t just discolor the stone—it actively degrades it. Acid rain, formed when pollutants combine with moisture in the atmosphere, further accelerates the breakdown of limestone and marble. The outer façade, which was once a pale cream color, had turned almost black in many areas before the most recent restoration efforts.

Starting in 2013, a major cleaning project removed centuries of pollution and grime from the exterior travertine. The work revealed the stone’s original color and halted further deterioration in the cleaned sections. But the pollution continues. Without ongoing maintenance and cleaning, the buildup will return.

Conservation teams now use advanced techniques, including laser cleaning, to remove pollutants without damaging the underlying stone. Protective coatings are being tested to shield vulnerable surfaces from future pollution. But as long as the Colosseum remains in the heart of a bustling city, air quality will remain a persistent threat.

Physical Wear from Foot Traffic

Between twelve and fifteen million people visit the Colosseum each year. Each one of them walks on floors, stairs, and surfaces that were built for durability but not for this level of sustained, concentrated use.

This kind of wear is most visible in high-traffic areas—the main staircases, the walkways along the perimeter, and the sections of the seating tiers that are open to visitors. In some areas, protective barriers and designated pathways have been installed to direct foot traffic away from the most fragile sections. In others, the original stone has been reinforced or replaced to prevent further damage.

The new arena floor project is designed, in part, to address this issue. By creating a retractable platform over the hypogeum, it will allow visitors to walk on a modern, load-bearing surface rather than directly on ancient structures. But, the tradeoff is that it will cover the currently “exposed ribs” of the hypogeum, removing the ability to see the building’s inner workings from the stands.

Balancing Access and Preservation

There is a constant tension between visibility and viability at the Colosseum. Not all of it is open to visitors, and the areas that are accessible change over time based on the condition of the structure and the needs of ongoing restoration work.

Certain sections are simply too fragile to allow public access. The upper levels, for example, are structurally unstable in places and require reinforcement before they can safely accommodate large groups of people. Other areas, like portions of the hypogeum, can only be visited with a guide because the passages are narrow, the footing is uneven, and the risk of damage—both to visitors and to the structure—is higher.

This creates tension. People want to see as much of the Colosseum as possible. But opening more areas to the public accelerates wear, increases the need for repairs, and raises safety concerns. The compromise is a system of timed entries, guided tours for sensitive areas, and periodic closures of sections that need maintenance or study.

What This Means for Visitors

When you visit the Colosseum, you’re seeing an active construction and conservation site as much as a historical monument. It will have scaffolding, barriers, and closed off sections. These can be viewed as frustrating interruptions to the experience, or as evidence that conservationists are hard at work keeping this site alive for your visit and for future visitors.