What Caused the Colosseum’s Asymmetrical Shape?

The Colosseum’s striking asymmetry — the intact four-storey northern façade and the lower, truncated southern side — is the direct result of the earthquake of 14 September 1349. The seismic event, which struck central Italy with devastating force, collapsed the southern portion of the Colosseum’s outer ring wall. The fallen stone was subsequently quarried for Rome’s great Renaissance and Baroque buildings, ensuring the damage was never repaired. The 1349 earthquake also caused major damage to the Basilica of Maxentius in the Forum, old St Peter’s Basilica, and several other classical and medieval structures across Italy. It is the single most consequential natural event in the Colosseum’s post-ancient history.

The 1349 Earthquake Quick Facts

  • Date: 9 or 10 September 1349 (contemporary sources vary)
  • Epicentre: central Apennines, in the area of modern Abruzzo and Molise
  • Estimated magnitude: approximately 6.5–7 on the modern moment magnitude scale
  • Impact on Rome: severe damage to classical monuments including the Colosseum, Basilica of Maxentius and old St Peter’s
  • Broader context: coincided with the Black Death pandemic then devastating Europe
  • Colosseum damage: collapse of the southern outer ring wall
  • Subsequent impact: fallen stone became a quarry resource for the next three centuries

What Actually Happened in 1349?

On 9 or 10 September 1349 — contemporary sources differ on the precise date — a major earthquake struck the central Apennines, with its epicentre in the mountainous region corresponding to modern Abruzzo and Molise. The shaking reached Rome with sufficient intensity to cause widespread structural damage, particularly to classical monuments that had been weakened by more than a thousand years of use and neglect.

The 14th-century poet Petrarch, living in Rome at the time, described the effects in letters. He recorded damage to churches, palaces and ancient monuments across the city. The Lateran basilica suffered significant damage. The bell tower of Old St Peter’s was partially destroyed. The vault of the Basilica of Maxentius — already ruinous after centuries of deterioration — lost additional sections. And the southern outer wall of the Colosseum collapsed.

The earthquake was not an isolated event. Central Italy experienced several major seismic events in the 13th and 14th centuries, and the region’s geological history includes a long succession of destructive earthquakes. What made 1349 particularly consequential for Rome’s classical heritage was the combination of magnitude, the already-weakened state of ancient structures, and the timing: the event occurred during the Black Death pandemic, when neither human nor financial resources were available for serious reconstruction.

Why Was the Southern Side More Vulnerable?

The question of why the southern outer wall collapsed while the northern side survived has been studied extensively and reflects a combination of factors. Geological evidence suggests that the southern foundations rest on softer alluvial soil — partly because the site originally held Nero’s artificial lake and the drainage works for that basin affected the ground composition differently on different sides. The firmer northern foundations, which rest on more stable subsoil, better absorbed the shock waves.

Engineering studies have also pointed to the direction of the seismic waves, which came from the south-east and transferred energy most destructively into the southern portion of the structure. Whatever the precise physics, the result is visible: the northern side preserves the original four-storey façade, while the southern side shows only the inner structural ring where the outer decorative wall once stood.

What Other Buildings Were Damaged?

Rome’s classical and medieval infrastructure was extensively affected.

Basilica of Maxentius

This massive Roman basilica, begun under Maxentius (reigned AD 306–312) and completed by Constantine, had already suffered deterioration over the centuries. The 1349 earthquake caused significant additional collapse of the vaulting, producing the ruinous but spectacular state visible today.

Old St Peter’s Basilica

The original St Peter’s, built under Constantine in the early fourth century, suffered structural damage including partial collapse of the bell tower. The building survived but was progressively weakened, contributing to the decision to demolish and rebuild it in the sixteenth century.

Lateran Basilica

The cathedral church of Rome, seat of the Pope as Bishop of Rome, suffered damage that required extensive later restoration. The papal residence adjacent to the Lateran was also affected.

Various Churches and Palaces

Contemporary sources list damage to numerous other Roman churches and residential buildings. The cumulative impact on the city’s built environment was substantial and contributed to the further contraction of active urban space in fourteenth-century Rome.

Why Wasn’t the Colosseum Repaired?

Three reasons. First, the Black Death. Europe was in the middle of the worst pandemic in its recorded history. The plague had reached Italy in 1347 and devastated populations throughout 1348–1349. Rome’s population, already reduced from its imperial peak, was further diminished. Neither labour nor financial resources were available for restoring damaged classical monuments.

Second, the papal absence. The Popes had relocated to Avignon in 1309 and did not return to Rome permanently until 1377. Throughout the mid-14th century, Rome had no effective central authority capable of commissioning or funding major conservation work on classical structures. The city was governed unstably by competing noble families and civic institutions, none of which had either the means or the interest to restore a pagan amphitheatre.

Third, the changed function of the building. By 1349, the Colosseum had not hosted public spectacle for more than 800 years. Its role had shifted to fortress, commercial space, burial ground and emerging Christian shrine. Restoring it to its ancient form was not a priority even for those Romans who recognised its architectural value. The collapsed stone was more useful as material for new buildings than as part of an intact monument.

How Did the Collapse Enable the Quarrying Era?

Directly and extensively. Before 1349, the Colosseum was a structurally intact building with some sections abandoned or repurposed. After 1349, it was a partially ruined structure with vast quantities of fallen stone available for extraction. This transformation made systematic quarrying both easier and more legitimate — the material was already on the ground rather than being pried from an intact façade.

The centuries that followed saw the Colosseum supply stone for major Roman building projects: Palazzo Venezia in the 1450s–60s, the rebuilding of St Peter’s Basilica through the sixteenth century, Palazzo Farnese under Michelangelo, Palazzo Barberini in the seventeenth century, and numerous churches and minor buildings. Much of Renaissance and Baroque Rome was built from material that had originally been cut for the Flavian Amphitheatre, fell in the 1349 earthquake, and lay available for reuse thereafter.

The quarrying only stopped in 1744, when Pope Benedict XIV issued a formal ban. By that point, approximately two-thirds of the original outer wall had been lost to the combined effects of the 1349 collapse and the subsequent four centuries of extraction.

Does the Earthquake Still Matter to Visitors Today?

Yes, in an immediately visible way. The single most striking feature of the Colosseum — the asymmetrical silhouette that gives the building its distinctive character — is directly the product of the 1349 earthquake and its aftermath. Walking around the perimeter, visitors move from the full four-storey northern wall to the lower, truncated southern side, experiencing in stone a specific moment of 14th-century disaster.

The contrast is also archaeologically valuable. The surviving northern façade preserves the original Flavian and Domitianic construction, allowing study of the building’s intended appearance. The southern side, with its exposed inner structure, reveals the engineering logic — the radial walls, the concrete vaulting, the hidden structural ribs — that would otherwise be invisible beneath the external decoration. A visitor sees both the monument as completed and the monument as engineered, in a single view.

Frequently Asked Questions

What year did the Colosseum collapse?

The southern outer wall collapsed in the earthquake of 1349, on 9 or 10 September. The rest of the structure survived the event, though progressively lost material to subsequent quarrying over the following centuries.

How much of the Colosseum fell in 1349?

The primary damage was to the southern portion of the outer ring wall. Initial collapse may have been followed by further deterioration and quarrying, so the precise immediate extent is hard to separate from the later losses. The visible absence today combines the 1349 collapse with centuries of subsequent extraction.

Did the earthquake destroy other Roman monuments?

Yes. Major damage was recorded at the Basilica of Maxentius, old St Peter’s Basilica, the Lateran Basilica, and numerous churches and palaces across Rome. The impact on the city’s classical and medieval heritage was substantial.

Why wasn’t the Colosseum repaired after 1349?

A combination of factors: the Black Death pandemic reducing labour and funding; the papal absence in Avignon, which removed central authority for major conservation; and the changed function of the building, which had long since ceased to be used as an amphitheatre and was not a restoration priority for medieval Rome.

Has the Colosseum had other earthquakes?

Yes. Central Italy is seismically active, and the Colosseum has experienced multiple earthquakes across its two-thousand-year history. Earlier seismic events in late antiquity caused the repairs that Domitian and later emperors documented. The 1349 event is the most consequential because the damage was never repaired.

See the Earthquake’s Legacy on a Guided Tour

Our Colosseum tours point out the physical evidence of the 1349 collapse and explain how it shaped the building’s subsequent history. Walking the perimeter from the intact north to the truncated south makes visible the single moment that reshaped the monument and the four centuries of quarrying that followed.