April 15-18, 2009
Indianapolis, Indiana, USA

Piero della Francesca On-line: Story of the True Cross, San Francesco, Arezzo (Italy)

Marilyn Aronberg Lavin, Princeton, New Jersey, USA; Kirk D. Alexander, IET Mediaworks, and Educational Technology, University of California, USA; Franco Tecchia, PERCRO, Scuola Superiore Sant’Anna, Pisa, Italy; and Marcello Carrozzino, PERCRO, Scuola Superiore Sant’Anna and IMT Institute for Advanced Studies, Lucca, Italy


In this paper we identify the art historical reasons for seeking to develop a 3-D, interactive, walk-through computer model for one of the greatest works of the Italian Early Renaissance. We further describe how the problem was solved and how it was made available to the public at large on-line.

Keywords: 3D graphics, Web 3D, Piero della Francesco, fresco painting, interactive, virtual reality, art

Looking at the Frescoes: Historical Background

St. Francis of Assisi came to Arezzo in the early years of the 13th century where he found a city torn with internal strife. With one of his many miracles, Francis brought peace to the community and blessed it with the vision of a great golden cross spreading its arms across the sky. As a result, his friars were allowed to congregate in a small community outside the walls and preach their message of love and salvation. By the early fifteenth century, the Franciscan Friary had moved into town where it built an imposing church dedicated to its founder. The apse end, rebuilt after a fire, was awaiting decoration. It was the custom in such establishments – always in need of financial support – to lease out space within the buildings to families to use as burial grounds. This privilege brought the friars monetary contributions for upkeep and/or enhancements of paintings, sculpture, and other church furnishings. The chapels on either side of the main apse had already been painted in the late 14th century, but the chancel itself, the Cappella Maggiore, which had been leased to the local Bacci family, was still without decoration.

After complaints from the friars in the 1440s, the Bacci sons sold a vineyard and other real estate to acquire the cash to begin paying for a campaign of fresco painting. As was usual, the administrators of the church, the Franciscans, were the ones who chose the appropriate subject matter, in this case, a subject dear to St. Francis’s devotion, the Legend of the True Cross. The apocryphal narrative was set on the three vertical walls of the chapel, with paintings on the triumphal arch and the vault creating a scheme of redemption under the authority of Papal Rome. Bicci di Lorenzo, an aging artist from Florence, was hired. He and his workshop started at the top (frescos are always painted from the top down because of dripping), completing a scene of the Last Judgement high up on the entrance arch, and the four Evangelists on the webs of the ribbed vault. Apparently during this operation, in 1452 Bicci di Lorenzo grew ill and returned to Florence where he died. Members of his shop continued the work for a short while, painting most of the decorations of the ribs and other structural members and at the least, two standing figures of the four Fathers of the Church that are just below the vault. Then they too left Arezzo. Only after this sequence of events was Piero della Francesca called in to complete the project.

Ever since the early 20th century when European artists took Piero as their favorite, he has had the reputation as the one Renaissance painter whose calm, forceful, and supremely imposing figures could be enjoyed by everyone without regards for their religious content. His high-toned colors, his geometrically perfect forms and spaces, his mesmerizing light flows and volumetric shadows satisfied the current visual hunger for simplicity, purity, and strength. In this vein, one critic even called him “the first Cubist”. In the 15th century, however, it was a different matter. Piero’s work, like that of almost all mid-15th century artists, served a religious purpose. As a result, there is no separation between what he represented and the way he represented it, between his form and his content. Moreover, while he was recognized as a maestro of painting, he was also honored as a great mathematician. The three important treatises he wrote (on algebra, geometry, and perspective for painters) are acknowledged as among the most important of his time. These interests are reflected in his paintings and may, to some extent, explain his appeal to the modern eye.

In spite of his current fame, it is somewhat surprising to find that there are no documents recording his Arezzo commission. We do not know when Piero was engaged (only that it was after 1452). We do not know what he was told to do (only that it was to paint the Legend of the True Cross, a subject used in many other Franciscan churches). We do not know who or how many men worked under him (although at least the name of one assistant, Giovanni di Piamonte, is known from other sources). And we do not know when he finished the job; we know only that in 1466 the frescoes were referred to in the past tense, and so we may assume that they were complete. Thus all the information we have comes the frescoes themselves. And they are some of the most challenging paintings of the Early Renaissance.

Figure 1

Fig 1: Interactive, 3-D, Walk-Through Model

The Legend and its Disposition

One of the most demanding aspects of the cycle is the way Piero arranged the scenes on the walls. Although the story of the Cross is of longue duré - a compilation of medieval legends beginning in the time of Genesis and progressing to the 7th century A.D. - it follows a simple chronological sequence. One might expect such a narrative told visually to "read" like pages in a book; that is, to start on the left at the top; move from left to right, and proceed down the walls, tier after tier. Piero chose not to tell the story in this manner, but to rearrange the sequence in a dramatic way. He placed his Genesis scenes not on the left, but on the right wall at the top and made them read "backwards" from right to left. He put the next episodes on the second tier and reversed the order to read left to right. He then had the story jump to the second tier of the right side of the altar wall and progress diagonally down to the lowest tier on the left side, and so on. Figure 2 shows how the "Narrative Sequence" continues in this "irregular fashion," ending, not at the bottom but at the top tier of the left wall!

The legacy of Piero's "rearranged" chronology has two parts:

  1. Jumping around the space reminds one of the chaotic rhythms of a medieval romance, the Roman de la Rose, for example. Such stories, which apparently St. Francis loved when he was a boy, are full of adventure, with stalwart knights and ladies fair, and always a moral overtone and religious goal. Their structures are full of surprising stops and starts, changes of direction, and what the modern mind considers to be irrational time changes. The Legend of the True Cross, as it developed, came out of this very tradition, and Piero did not want his viewers to forget this fact.
  2. At the same time, Piero’s arrangement makes the story take on another character, one that is abstract in nature and serious in implication. The two lunettes at the top of the side walls match, showing the beginning and the end of the story, each centered in the wood of the cross. The second tiers match; they express the power of royal women who are divinely inspired to recognize the holy wood. On the altar wall, scenes on either side of the window match: the top tiers show Old Testament prophets who foresaw the coming of Christianity and the story of the cross; the second tiers represent a form of comic relief with serious undertones. They are genre scenes of every day that allude to Christ’s passion and the Eucharist. The bottom tiers also match. Both are scenes of annunciation: one of the birth of Christ, the other the birth of Christianity. The bottom tiers on the side walls match. They are scenes of battle: one is a bloodless victory over fellow Romans at the sign of the cross, and the other is a bloody battle for victory over the blasphemous infidels. Figure 3 shows this "Thematic Balance." The effect of this new arrangement creates the symmetry and balance, the gravity and dignity required by Aristotle and Horace for creating epic poetry. By dint of his re-organized disposition, Piero achieved what might be called the first modern epic.

Figure 2

Fig 2: Narrative sequence

Figure 3

Fig 3: Thematic balance

Our Project

We have just presented the fresco cycle's "pattern(s) of disposition" in the traditional manner; that is, with diagrams. This technique is helpful but lifeless and entirely antiquated. Our goal was to find a way to modernize the whole procedure. To do so, we created an Interactive Computer Model that is now available on-line, free of charge, so that the viewer can move through the space of the chapel to follow the sequence(s) as Piero conceived them. Remember, he never had a chance to see the frescoes in this manner. While he was working, the chapel was full of scaffolding, and he would have had no way to step back for a general view. And even Piero couldn't fly. At the same time the Model provides high-resolution images of all the paintings, scanned from photographs taken after the recent restoration campaign, some of which were carried out in 1:1 proportions.

Figure 4

Fig 4: Photograph taken on scaffolding

Figure 5

Fig 5: Model Screen-Shot

Brief History of the Project

In our quest to improve the viewing of large-scale fresco paintings in monumental buildings - studying the paintings and keeping their context - the first fifteen years were carried out at Princeton University. Working with Kirk D. Alexander and members of his staff at Princeton University’s then new Computer Center, by 1992 we had developed a computer model in which it was possible to navigate throughout the chapel, follow the patterns of disposition, and study the paintings in detail. We attached audio commentary for each scene, giving both art historical and technical information. The equipment at that point was the Silicon Graphics VGX IRIS workstation and early versions of Oracle and Traveler. By 1995, we used this equipment for an art history seminar in a classroom with 24 workstations.

As time went on, with new technical developments it became possible to run the model from a CD and show it on a normal PC, and finally on a LapTop. This improvement made it easier to display the Model and use it for lectures and classes in “smart” classrooms that were developing in increasing numbers. In 1999 I made arrangements with the Superintendent of the Ministry of Fine Arts in Arezzo whereby new photographs taken by Alessandro Benci, official photographer of the Ministry, could be mapped into the Model in exchange for permission for the Ministry to show the Model for its own purposes. The arrangement was made with the understanding that each entity would acknowledge the contribution of the other at each showing. The Ministry mounted the Model in two workstations in the church of San Francesco in Arezzo for use by visitors after they had been through the church and had seen the frescoed chapel itself.

Although this achievement was very gratifying, we still felt that the number of viewers was too restricted, limited to individual lectures and travel to Arezzo. The first step in our search for a broader public was to achieve independence. In 2000, Princeton University relinquished all copyright claims on the Model and the Arezzo Ministry gave free use of the photographs for non-profit purposes. Lavin, Alexander, and Benci became the “authors” of the Model, responsible for its use and its dissemination.

Our final goal was realized in August of 2008. After all these many years of work, the Piero cycle of the True Cross is on the Web, available to the public with all its bells and whistles. By good luck Kirk, at the 2007 conference of Museums and the Web (Archives & Museum Informatics) in San Francisco, CA, met two member of the Scuola Superiore Sant’Anna in Pisa, Italy: Franco Tecchia and Marcello Carrozzino. In conversations with them, he discovered that they work precisely in the field of 3-D virtual reality and in mounting cultural heritage material on the Web. Kirk solicited their help and after various meetings, they enthusiastically joined our project.

To mount the model on the Web, Marcello obtained the use of the XVR ActiveX plug-in from its parent company, VRMEDIA s.r.l, and he constructed many important new enhancements. XVR is a technology that was created for the development of Web-enabled virtual reality (VR) applications (Carrozzino et al, 2005). In recent years it had evolved into all-round systems software for interactive applications. Supporting a wide range of VR devices and using a state-of-the-art graphics engine for the real-time visualization of complex three-dimensional models, XVR enables the function of applications ranging from simple 3D Web presentations to advanced off-line VR installations.

As opposed to VRML products, which are based on a simple declarative language, XVR-driven applications use a dedicated scripting language whose concepts and commands are specifically targeted at VR. As a result, in the on-line version of the Model, interaction with the viewer is more flexible, responsive, and visually effective.

When connecting to the Piero model URL, the browser downloads the XVR plug-in; this happens only once. Subsequently, the application data are downloaded and stored in a local cache, in order to speed future connections. The application also allows for free navigation throughout the model and provides a graphic user interface (GUI) which is embedded in the 3D window and implemented within XVR for user interaction. An interesting side effect is that XVR is also able to drive immersive instalations. As a result, with minimal configuration changes, the application may be experienced on stereoscopic devices like Head Mounted Display, CAVE-like systems, and so on.

Figure 6

Fig 6: Immersive navigation of the model

At this time, the application is fully available on the Internet Explorer browser at

There is a separate page containing all the high-resolution still images that is open to users with all browsers.

Figure 7

Fig 7: Splayed view of Chapel; high resolution images available with double click

Placing the Model on the Web required forfeiting a certain amount of resolution in the 3D-model. But at the same time, the embedded high resolution images, now accompanied by further historical material, are better than ever since they can be manipulated with the ZoomIt program that brings detailed viewing to an ever higher level of quality. The Institute for Advanced Study, Princeton, NJ, is generously hosting the site. At the moment, the audio commentary is available in English. We hope, in the near future, to have a mirror site with commentary in Italian, hosted on Marcello’s side of the Atlantic Ocean to speed the download for our European visitors.


Carrozzino, M., F. Tecchia, S. Bacinelli, C. Cappelletti, and M. Bergamasco (2005). Lowering the development time of multimodal interactive application: the real-life experience of the XVR project. In Proceedings of the 2005 ACM SIGCHI international Conference on Advances in Computer Entertainment Technology. (Valencia, Spain, June 15 - 17, 2005). ACE '05, vol. 265.

Lavin, M.A. (2002). Piero della Francesca. London: Phaidon Press.

Cite as:

Lavin, M. A., et al., Piero della Francesca On-line: Story of the True Cross, San Francesco, Arezzo (Italy). In J. Trant and D. Bearman (eds). Museums and the Web 2009: Proceedings. Toronto: Archives & Museum Informatics. Published March 31, 2009. Consulted aronbergLavin/aronbergLavin.html