Those enigmatic lead-clad reptilian forms over there are Renzo Piano's designs for 21st-century Roman concert halls. We look at how the architect came by his extraordinary concept, and how it works in practice.
They squat like a family of colossal tortoises in a forest glade. All three are encased in grey, armoured shells made up of myriad lead panels. It is only beneath these carapaces that low strips of glazing offer glimpses into the soft hearts of these enigmatic structures.

The three buildings together make up Rome's £100m concert hall. The Eternal City had been lacking a major concert hall since 1936 when the last one, converted from Emperor Augustus' mausoleum in 1908, was ripped out by Mussolini in his zeal to restore ancient Rome. The very belated replacement, which held its inaugural concert just before Christmas, was fittingly designed by Italy's greatest living architect, Renzo Piano. It is in fact the Genoese architect's first building in Italy's capital.

The design by the Renzo Piano Building Workshop was selected through an international competition held in 1993. Piano has a special affinity for musical auditoriums: he has been responsible for six. His first was the IRCAM musical research institute, part of Paris' Pompidou Centre, which he designed with Richard Rogers in 1971. Piano likens the process of building a concert hall to making a violin. "In the end it is still about building instruments for making music or for listening to music," he says. "Sound is king, and the resonant chamber has to be tuned for vibrating with those frequencies and energies."

For the Rome project, Piano has revolutionised the concept of the multiple concert hall. He rejected the notion contained in the competition brief for a megastructure combining several halls, like the National Theatre in London. Instead, he separated out the three halls and set them up as a collection of free-standing pavilions rising out of a common podium.

The halls themselves range in size from a 700-seat venue for concert operas and chamber music to a 2800-seat symphony auditorium, the largest a concert hall can be stretched to without sacrificing high-quality natural acoustics. The podium below contains a continuous foyer serving all three halls, an exhibition hall, two large rehearsal halls and a restaurant, along with a number of spaces for recording, conferences, teaching, research, retail and services. Far more than a concert hall, this is, as Piano claims, a veritable "city of music".

An obvious architectural family is formed by the three scaly shells, but Piano prefers the more functional analogy of musical instruments, citing the lute as an example, which is "inspired by the form and use of wood". The curving roofs of the two smaller halls are supported on large timber and plywood trusses. Piano also likes to cultivate a more architectural analogy for his massive, impassive forms. "They could be some of Piranesi's ruins, a metaphor for classical antiquity," he says. The long-lasting, natural materials of the lead cladding of the shells, the narrow red bricks of the podium and internal walls, and the travertine marble of the podium deck, amphitheatre tiers and foyer flooring are all in the ancient Roman tradition.

Separating out the three auditoriums has the obvious advantage of preventing sound transference between them. And, free from being hemmed in by the others, it allows each hall to assume its natural form. As well as these architectural advantages, the development offers three significant urban design benefits, two of which were not envisaged in the competition brief.

Rather than being crammed into Rome's congested city centre, the complex was blessed with a 5 ha site situated in scruffy parkland where Rome's Olympic Village was built in 1960s. Piano has liberated the complex of buildings to spread out and merge into the surrounding park. The first design bonus is the rejuvenation of the parkland by the addition of the complex's open-air spaces, which are permanently open to the public, and by the planting of 400 more trees. The moulded lead shells of the concert halls stand as a trinity of giant sculptures, and fitting neighbours to the glass and concrete dome of Nervi's Olympic Pallazzo dello Sport. In Piano's words, the halls are "three resonant chambers that seem to swim above a sea of vegetation". The combination of culture and landscape is reflected in the official name given to the complex by the city council: Park of Music Auditorium.

As with every new development in a historic city, the site was subjected to archaeological excavations between initial design and start of construction. But, this being Europe's greatest ancient city, an entire Roman villa dating back to the 4th century BC was unearthed. The city council decided to preserve the remains in situ and make them publicly accessible – luckily Piano was able to oblige and still remain true to the original design concept. The competition-winning scheme consisted of a horseshoe arrangement of halls, but after the villa was discovered, these were teased out to make three distinct fingers at right angles to each other. The ancient remains fit neatly into the open-air gap between two of the fingers.

The second advantageous side-effect of Piano's configuration is that it not only preserves the ancient remains but presents them as a fully accessible key element of the complex. In addition, ancient clay pots and other artefacts discovered on the site are conveniently displayed in the podium exhibition hall overlooking the open-air remains.

The third urban design benefit is the creation of a free fourth performance venue within the complex, which serves as a public piazza when not in use. This is a semi-circular open-air amphitheatre seating 3000, which has been carved out of the podium linking the three halls.

Piano's design can be criticised for the persistent stylising of the zoomorophic shells, which cut across his pedigree for inspired functionalism. In the largest hall, the bulbous form of the lead shell is the true outline of the interior's fan shape, but the other two halls have more rectilinear forms, and the bulging lead shells conceal straight external brick walls behind, creating pockets of dead space in between.

Despite this architectural conceit, Rome's three musical tortoises set an inspired new model for the design of concert halls, and show how the arts of music, architecture, sculpture and landscape can be orchestrated together in the cause of urban regeneration.

Orchestral manoeuvres in the light

An elaborate exercise of designing the three concert halls around the desired acoustic properties was carried out by Piano’s team, working with acoustician Helmut Müller of Munich. First, small models with reflective surfaces were built, and the routes followed by light reflections were traced using lasers. Data was then fed into a computer to simulate the reflections of sound waves. Finally, real sound waves were tested in large models, some as big as a room. The grand auditorium
Containing 2756 seats, the largest hall is at the upper limit for high-quality natural acoustics: any bigger and the back rows would be overwhelmed by echo. It is intended for symphony concerts with large orchestras and choir. A terraced fan-shape, which the Italians call like a vineyard, has been adopted to emulate other grand concert halls. Acoustic panels resembling giant cushions and composed of terracotta bricks sandwiched between MDF panels help achieve the optimum reverberation time of 2.2 seconds. The adaptable hall
The medium-sized hall, which has 1200 seats, was designed to cater for orchestral and choir concerts, ballets and contemporary music recitals. The stage and the seating can be adapted to different types of performance. Sound is diffused in the rectangular auditorium by convex wall panels of dense concrete sandwiched in mdf. The intimate theatre
The smallest hall seats just 750, offers maximum flexibility and can stage chamber music concerts, plays and conferences. As in a traditional theatre, it comes equipped with a fly-tower to store scenery and an orchestra pit, and hinged panels at either side of the stage can be folded out to create a proscenium arch.