One of the least-known aspects of the Colosseum is that it was not an open-air building in the modern sense. On intensely sunny days, an extraordinary piece of engineering — the velarium — shielded 80,000 spectators from direct sunlight, transforming the experience of the munera from a summer ordeal into a relatively comfortable spectacle. Exactly how the system worked is still being researched, but its physical traces remain visible on the Colosseum's walls today.
What the Velarium Was
The velarium (from Latin velum, "sail, cloth") was an enormous awning, or system of awnings, that was spread over the Colosseum's seating area to shade spectators during the hottest hours. It was not a fixed roof: it was a system of ropes and cloth panels that could be deployed, adjusted and retracted depending on weather conditions.
Ancient sources describe the velarium as one of the features most appreciated by Roman audiences. The poet Martial, who attended the games in the Flavian amphitheatre, praises its use in several epigrams. Pliny the Younger and Juvenal cite it as a defining feature of the great spectacles.
It is important to note that the velarium did not cover the entire structure: the sand surface (the arena proper) remained open, both to allow adequate lighting for the fights and to permit the circulation of air needed to ventilate the hypogeum below. The coverage extended over the cavea — the tiered seating area where the spectators sat.
The Physical Evidence: The Corbels of the Fourth Floor
The most tangible physical evidence for the velarium's existence is still visible today on the Colosseum's crown: a series of 240 stone corbels projecting from the wall of the fourth order (the attic storey), arranged at regular intervals around the entire circumference of the amphitheatre.
These corbels — technically known as asolette — were the supports into which the poles (arbores) that held up the velarium's rope system were inserted. The fact that they survived medieval plundering and centuries of spoliation is a testament to their structural solidity: they were fully embedded in the wall rather than simply set against it.
Similar corbels and pole sockets are found at many other Roman amphitheatres across the Empire — at Arles, Nîmes, Pozzuoli, Capua — suggesting that the velarium system was a standardised technology spread throughout the Roman world, not an invention exclusive to the Colosseum.
Who Operated the Velarium: The Sailors of Misenum
The most precise ancient source on the personnel who ran the velarium is the chronicler Cassius Dio: the system was operated by sailors from the imperial fleet stationed at Misenum (modern Misenum, on the Bay of Pozzuoli, in northern Campania).
These soldier-sailors (classiarii) were a specialised detachment permanently assigned to Rome for the needs of public spectacles. Cassius Dio gives a figure: operating the Colosseum's velarium required approximately eight thousand men. Even if this number is a rhetorical exaggeration, the scale of organisation required was extraordinary nonetheless.
Why sailors? The answer is intuitive: the handling of large sails, ropes, windlasses, and canvas rigging systems was pre-eminently a naval skill. Rome's fleet sailors were the sector professionals, trained daily in deploying, furling and adjusting large surfaces of cloth under wind conditions and time pressure.
The Rome detachment was physically housed in barracks around the Colosseum — probably in connection with the adjacent structures whose traces survive in today's Rione Celio district.
The Mechanism: Poles, Ropes and Cloth
The exact reconstruction of the velarium's mechanism is one of the open problems of ancient Roman architecture. Written sources describe the outcome but rarely the process; physical evidence permits deductions but not certainties. The main hypotheses developed by scholars across the twentieth and twenty-first centuries converge on a basic model:
The Outer Poles (Arbores)
From the 240 fourth-floor corbels rose an equal number of wooden poles — probably fir or larch, lightweight and strong — projecting inward over the upper edge of the seating area. The estimated length of these poles was 7–12 metres.
The Master Ring-Cable (Corona)
A ring cable was strung in tension across the top of the poles, running around the full circumference of the amphitheatre and held in tension by the poles themselves. This ring cable served as the primary anchor for the entire system.
The Radial Ropes and Central Opening
From the ring cable ran radial ropes converging toward the centre of the arena, where a central ring (estimated between 6 and 14 metres in diameter depending on the scholar) tied them together. By remaining open, this ring allowed light to fall on the sand and permitted heat and smoke to escape.
The Cloth Panels (Vela)
The covering panels were hung from the radial ropes, creating a continuous surface resembling the sail of a ship but laid horizontally. The material was probably linen or double wool, possibly treated to be water-resistant. The total covered surface area is estimated at approximately 24,000 square metres — comparable to three full-sized football pitches.
The Operating System
To open and close the velarium, the radial ropes were connected to a system of windlasses positioned at the base of the seating tiers or in dedicated recesses. The operation required coordinated action by many workers acting simultaneously across different sections of the circumference.
The Velarium and Wind: The Main Challenge
The critical challenge was not deploying the velarium on calm days, but maintaining it in windy conditions. Cloth of those dimensions, exposed to wind, generates enormous lateral forces — enough to topple poles, snap ropes or tear the fabric.
Solutions probably included:
- Strong radial pre-tension that loaded the system and reduced the wind effect
- A reefing system analogous to the nautical practice of taking in sail, allowing the exposed surface to be reduced on windy days
- The ability to retract the velarium entirely in high winds, leaving the seating uncovered
This would explain why several ancient sources mention performances disrupted or made uncomfortable by wind: the velarium was not always in operation.
The Velarium at Other Roman Amphitheatres
The Colosseum was not the only amphitheatre with a velarium. The technology was spread across the Empire, adapted to local scale and resources.
Arena of Nîmes (Gaul): one of the best-preserved provincial amphitheatres, it still retains the corbels for the velarium poles on its external crown.
Arena of Arles (Gaul): the same system; after the end of the Empire it was converted into a medieval fortress and then an inhabited quarter — a testament to the structural longevity of Roman amphitheatres.
Amphitheatre of Pozzuoli (Campania): close to the Misenum fleet base, it could presumably also draw on specialist sailors for the velarium.
Theatre of Pompey (Rome): the first permanent theatre in Rome, built by Pompey in 55 BC, had a similar shade-cloth system — also operated by sailors — and is cited in the sources as an antecedent to the Colosseum's velarium.
The Academic Debate: Competing Hypotheses
The velarium question has generated serious research since the nineteenth century. The main points of debate are:
Full or Partial Coverage?
Most scholars agree that the velarium could not cover the seating area entirely: the physics of cloth at those dimensions and the system of radial ropes always imply a central opening. The diameter of that opening is the crux of the argument. Proposals range from a minimal opening of a few metres to an opening of 14–15 metres. The most widely accepted hypothesis today places the opening at approximately 8–10 metres across.
The Material
Some research has proposed that the panels could have been silk or treated plant fibres rather than linen alone. Evidence of organic residues in the fourth-order zone is sparse and inconclusive.
Continuous Surface or Wedge Segments?
An alternative hypothesis, advanced by some engineers who have studied the system, proposes that the panels did not form a continuous surface but rather a series of separate triangular wedge segments, each independently controllable — a more flexible but less shade-efficient arrangement.
The Strandberg Model
In 2015, Swedish researcher Karl-Erik Strandberg published a detailed reconstruction of the system based on engineering calculations that accounted for tension forces, estimated cloth weight and wind resistance. His model, featuring panels with parabolic curvature supported by a network of secondary ropes, has been widely cited in subsequent scholarship.
What Survives Today
Of the 240 original fourth-floor corbels, approximately 40–50 survive in their original or near-original positions. The majority were lost during the medieval and Renaissance centuries of spoliation, when the fourth storey was systematically dismantled to recover valuable marble and fired brick.
The surviving corbels are most visible in the north and west sectors of the crown, where the structure is best preserved. It is not normally possible to approach the fourth-floor level on a standard ticket; the belvedere route (included in the Full Experience) allows some corbels to be observed at relatively close range.
Reach the Colosseum with Your Private Driver
Discover every detail of the Colosseum — from the velarium to the hypogeum — with your own private NCC driver. Transfers from Fiumicino, personalised tours of ancient Rome. Professional service from €49. → Book your driver at myromedriver.com
Frequently Asked Questions
Did the velarium also cover the arena floor (the sandy surface)? No. The velarium covered only the cavea — the tiered seating area. The central arena remained open for lighting and ventilation reasons.
How many people were needed to open the velarium? Cassius Dio mentions approximately eight thousand sailors. This figure probably includes maintenance and guard staff as well as the operators directly working the velarium.
Was the velarium always open during events? No. In strong winds it was reduced or retracted entirely. Ancient sources record performances held in full sun without coverage.
Are there attempts to reconstruct the velarium? Yes. Over the years various research groups have produced computer models and scale prototypes. No full-scale physical reconstruction project has been authorised for the Colosseum itself; other sites, such as the Nîmes arena, have experimented with similar temporary structures.
Could the velarium also serve as protection from rain? Probably yes, though ancient sources do not explicitly name rain protection as a primary function. Sun protection was the main stated purpose.
How can you see the velarium corbels today? The corbels are visible on the Colosseum's external crown, especially in the better-preserved sectors. From ground level with a good telephoto lens they can be clearly distinguished. From inside at the fifth-floor level (the belvedere route) a few can be observed at relatively close range.
Article No. 5 — TIER S — MON-01 Colosseum Type: HISTORY Words: ~2,400