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Introduction

Even today, in a world of skyscrapers, the Colosseum is hugely impressive. It stands as a glorious but troubling monument to Roman imperial power and cruelty. Inside it, behind those serried ranks of arches and columns, Romans for centuries cold-bloodedly killed literally thousands of people whom they saw as criminals, as well as professional fighters and animals.

Indeed, it was the amphitheatre's reputation as a sacred spot where Christian martyrs had met their fate that saved the Colosseum from further depredations by Roman popes and aristocrats - anxious to use its once glistening stone for their palaces and churches. The cathedrals of St Peter and St John Lateran, the Palazzo Venezia and the Tiber's river defences, for example, all exploited the Colosseum as a convenient quarry.

As a result of this plunder, and also because of fires and earthquakes, two thirds of the original have been destroyed, so that the present Colosseum is only a shadow of its former self, a noble ruin.

The Colosseum was started in the aftermath of Nero's extravagance and the rebellion by the Jews in Palestine against Roman rule. Nero, after the great fire at Rome in AD 64, had built a huge pleasure palace for himself (the Golden House) right in the centre of the city. In 68, faced with military uprisings, he committed suicide, and the empire was engulfed in civil wars.

The eventual winner Vespasian (emperor 69-79) decided to shore up his shaky regime by building an amphitheatre, or pleasure palace for the people, out of the booty from the Jewish War - on the site of the lake in the gardens of Nero's palace. The Colosseum was a grand political gesture. Suitably for that great city, it was the largest amphitheatre in the Roman world, capable of holding some 50,000 spectators.

Eventually there were well over 250 amphitheatres in the Roman empire - so it is no surprise that the amphitheatre and its associated shows are the quintessential symbols of Roman culture.

Construction planning

Emperor Titus  © The Colosseum was opened in AD 80 by Vespasian's son and successor, Titus. Given the scale of the enterprise it was built remarkably quickly. And given the site, in a valley where there was previously a lake, it had to be planned carefully.

For example, drains were built 8m (26ft) underneath the structure, to take away the streams that flow from the surrounding valleys and hills. Then foundations, roughly in the shape of a doughnut, made of concrete: under the outer walls and seating, they are 12-13m (39-42ft) deep, while under the inner ellipse of the arena, they are only 4m (13ft) deep, and designed in strips beneath each of the concentric walls. Even in this grand design, costs were carefully controlled.

I cite these figures to illustrate the scale of the enterprise and the forethought that went into the design. Over-engineered perhaps, but it has stood the test of time. The spoil from the huge hole dug for the foundations was used to raise the surrounding ground level by almost 7m (23ft), on top of the 4m (13ft) from the debris of Nero's fire, so that the new amphitheatre stood up higher in its valley site. The design advantage of looking up at, rather than down on, the amphitheatre is obvious.

The name of the architect is unknown, but by analogy with what we know from elsewhere in the ancient world, the design process would have involved floor plans drawn to scale, 3-dimensional scale models, perspective drawings, and for the artisans some full-size design sketches.

The basic point being emphasised here is that in this building of huge scale and complexity, much of the detail was worked out before the building started. Indeed the building was created according to a set of architectural principles, or a set of conventions developed in the construction of other amphitheatres.

Design details

Rome's Colosseum interior  © The basic design units were multiples of 20 Roman feet (the Roman foot varied, but was around 29.6cm). These conventions were adjusted according to the demands of each site, but the basic pattern is repeated, and much of it is not easily visible to the naked eye.

Our unknown architect apparently began with the idea of building an arena measuring 300 x 180 Roman feet. The ideal ratio of the period was considered to be 5:3. By convention also, the width of the auditorium equalled the width of the arena, and in the Colosseum, it also surprisingly equalled the height of the external facade. These symmetries probably impressed both architect and emperor.

So the total length of the Colosseum was originally planned, according to one convincing reconstruction, as 660 Roman feet long (300 + 360) and 540 Roman feet wide The perimeter can be roughly calculated as (L + W) x /2 or 1,885 Roman feet (or more precisely, using trigonometry).

Did the perimeter size matter? Yes, because the perimeter had to be split up among a grand number of equally sized entrance arches (both Capua and the Colosseum had 80 entrance arches, Verona and Puteoli 72 etc).

Entrance arches in grand amphitheatres were 20 Roman feet wide, with 3 Roman feet extra for the columns in between. So the Colosseum received a perimeter of 1,835 Roman feet (80x 23 =1840), and the arena was adjusted to 280 x 168 (still 5:3).

Similar numerical patterns can be seen in the Colosseum's famous façade. For example, the height of the two middle stories is twice the inter-columnar width. Or seen another way, the horizontal gap between the piers (15 Roman feet) equals the vertical height from the pier to the springing of the arch.

Harmony

Arches on the Colosseum  © So we are confronted visually with a series of squares within the framing of the arches. These are not accidents, but details of design, which reflect the architect's preoccupation with principles of number, and provide the viewer (however unconscious he or she may be) with a steady and harmonious rhythm in the façade.

The ordered beauty and formal regularity of the Colosseum's exterior is created by three storeys of superimposed arches with engaged (ie semi-circular) columns. These columns are of different orders on each storey (Tuscan at the bottom, then Ionic, with Corinthian columns in the third storey). The fourth higher blind storey is punctuated by pilasters, decorated with Corinthian capitals.

In between the pilasters, are small rectangular windows. Above and between the windows there are stone socles (plinths), which once held the masts used to support the awnings, designed to shade about one third of the spectators (the length of the horizontal poles was limited by the length of Mediterranean pines and the weight of the awnings). If you look upwards, you can still see the holes through which these vertical masts slotted.

The exterior was decorated at the top with glistening gilded bronze shields, and the arches were filled with painted statues of emperors and gods. Two grand entrances, one at each end of the minor axis, were used by the emperor, as well as by official presenters of shows and no doubt by other grandees.

The entrances were marked by giant porticoes, each topped by a gilded horse-drawn chariot. The emperor also had a private entrance, which went under the seats, and emerged in the imperial box.

Spectator experience

Detail of a gladiator and leopard from a Roman mosaic  © Spectators found their way to their seats through arches numbered I - LXXVI (1-76). The four grand entrances were not numbered. The best seats were on or just behind the podium, raised for safety's sake two metres above the arena; animals and gladiators were kept out by a further fence just inside the arena, which helped to ensure that the action was in everybody's view.

Inside the amphitheatre, but at its outer rim, there were, at the first three levels, grand circular promenades, though as you went upwards the dimensions became smaller and the decoration less grand. At the first level, the floors were of marble or Travertine (the stone from which the outside walls were made), while the walls were of polished marble slabs and the ceilings of painted stucco.

Their present grim decoration does not do them justice - and the exterior, pockmarked with holes made by medieval robbers looking for iron clamps, gives no real indication, either, of what the building looked like in antiquity.

Inside the auditorium, except for the front rows on the podium, spectators were packed like sardines in a tin. Evidence from other amphitheatres suggests an average of 40cm width per spectator and 70cm legroom, which makes an economy class airline seem generous.

The entrances and staircase were arranged with the help of marble and iron dividers - to keep different classes of clientele separate. Indeed, the very top section of the Colosseum is separated from other spectators by a 5m- (16ft-) high wall.

Modern scholars often say that the hierarchy of seating mirrored the social hierarchies of Roman society. But we should be cautious. The five sections of the auditorium, from bottom to top, would have contained only about 50,000 predominantly adult males out of an adult male population in the city of Rome of close on 300,000.

The lower class population of Rome was seriously and systematically under-represented. And the two lowest (ie most prestigious) sections of the auditorium accommodated, respectively over 2,000 and almost 12,000 spectators, numbers which do not coincide with any known social groups, such as senators (600) or knights (perhaps 5,000).

Those in the top rows had shade, while nobles sweated in the sun; but those at the very top, which would have included women and the poor, were a good 100m from the centre of the arena. The myopic presumably just sat and heard the crowd roar.

The arena

The arena itself was probably covered by a good 15cm of sand (harena), sometimes dyed red to disguise blood. And, as is evident in Ridley Scott's film Gladiator (2000), the arena was dotted with trap-doors designed to let animals leap dramatically into the fray. The arena was also sometimes decorated with elaborate stage scenery, so that the ritual murder could be varied with theatrical tales.

The Colosseum's partial destruction allows us to see into the bowels of the amphitheatre, in a way that no ancient could. But when the Colosseum opened in AD 80, Titus staged a sea-fight there (in about one metre of water), and recent research has shown convincingly that the amphitheatre had no basement at this time.

But the rivalrous brother of Titus, Domitian (emperor 81-96), was quick to have a basement built - with ring-formed walls and narrow passages. In this confined space, animals and their keepers, fighters, slaves and stage-hands toiled in the almost total darkness to bring pleasure to Romans.

A series of winches and the capstans would have allowed teams of slaves to pull in unison and hoist heavy animals from the basement to the main arena, and this machinery has been reconstructed, in part, from ancient drawings - aided by the bronze fittings that still survive in the basement's floor. The rope-burns of the hoists are still visible in the stone of the lift-shafts.

Overview

For all its outside trappings in once glistening local travertine stone, the Colosseum was really a triumph of brick-vaulting and cement. Structurally, the building works by a robust balance of pressures.

The huge downward vertical thrust of the external walls matches the outwards thrust of the barrel vaults in the circular promenades, which was itself also relieved by the series of radial walls, built like the spokes of wheel, from the inner ring of the arena. And the sideways thrust of the high heavy stone wall is dispersed via the superimposed rows of arches and compensated by the circularity of the building.

The construction is strikingly different from most Greek and Roman public buildings. They followed the classic model of Greek temples, with their rectangular rows of columns, topped by beams and relieved by a triangular pediment.

The invention of arches and vaults, made of brick-faced concrete, allowed Roman architects much greater spans - and more visual variety. Hence the Colosseum's elaborate honeycomb of arches, passages and stairways, which allowed thousand of spectators to get into and watch their murderous games in a custom-made amphitheatre. And the Colosseum's imposing exterior was then, as it still is, a marvellous monument to Roman imperial power.

Find out more

Books

The Colosseum by A Gabucci (Los Angeles, 2000)

Roman Builders by R Taylor (Cambridge, 2003)

The Principles of Roman Architecture by Mark Wilson Jones (New Haven, Conn., 2000)

The Story of the Roman Amphitheatre by D L Bomgardner (London, 2000)

About the author

Keith Hopkins is Emeritus Professor of Ancient History at the University of Cambridge, and Fellow of King'College. His publications include A World Full of Gods, Death and Renewal and Conquerors and Slaves.