The tragic loss of lives in the Church of San Francesco in Assisi has - very naturally - obscured the actual degree of damage to the building and its art treasures. We still do not know exactly what has been destroyed, what has been merely damaged and what - if anything - has been left untouched.

The church is a unique place, not only because it is the burial place of St Francis but because it is one of the forcing grounds of Western art. On its walls and ceilings were created the works which mark the end of European subjection to Eastern art and ideas and the emergence of Western realism. Many or most of Italy's greatest early masters worked there under the patronage of the popes.

St Francis himself was born locally, the son of a cloth dealer. He was baptised Giovanni but perhaps because of his mixed parentage was called Francesco, the "little Frenchman". He seems to have been a sociable young man, fond of parties and music-making, before he suddenly gave up his way of life and became a mendicant preacher and ascetic.

Francis soon attracted followers, so he set up a kind of informal brotherhood which he called "Fratres Minores". This was to become the Franciscan Order as we know it. It was formally recognised by Pope Innocent III and was given preaching rights. This was essentially a politic move; the papacy was alarmed by the many lay Christian movements and heresies of the time, and it wanted to keep them under direct clerical control.

Francis died in 1226, aged about 43. Miracles were soon attributed to him and he became such a cult figure that Pope Gregory IX was virtually forced to canonise him. The next step was to build a monumental church in his honour and where his body could be ritually reburied. Once again, the papacy kept a close grip on things. In 1253 the building was completed and the Pope consecrated the altars and church before a vast crowd.

San Francesco is built on a hill and is in two parts, the Upper and Lower Churches. Ironically, the site on which it stands had been used for executions in the Middle Ages and was popularly known as "The Hill of Hell". The next step again was to decorate it properly. The papacy donated various treasures, superb stained glass windows were commissioned and the greatest painters of the day were called in to work there. Italy was wracked at this time by the ongoing feud between the popes and the Hohenstaufen emperors. Nevertheless work went on steadily over decades and its first high point was the decoration of the Upper Church by Cimabue, a Florentine painter whose real name was Cenni di Peppi. Cimabue is a rather mysterious figure (although Dante mentions him) but he had worked in Rome and so was known to the popes. His frescoes, alas, are terribly decayed - the ghosts of what must have been some of the greatest works of the later Middle Ages. Cimabue, instead of working in the pure fresco manner, touched up most of his murals a secco, which probably explains why they have not lasted physically.

As late as the mid 16th century Giorgio Vasari, the Florentine painter and author of Lives Of The Painters wrote: "This truly great work by Cimabue, so richly and skilfully executed, must in my opinion have astounded everyone at that time, especially as the art of painting had been completely unenlightened for so long."

Cimabue has proved to be a star-crossed artist. One of his few surviving works, a crucifix, was very badly damaged in the Florentine floods of 1967. Now only a tiny handful remains from the output of a supreme master.

Cimabue probably worked at Assisi from about 1280. In the last six years of the century another great Florentine, Giotto, then about 30 years old, worked with a team of assistants in the nave of the Upper Church. Here he painted 28 scenes from the life of St Francis and in these he broke with the hieratic, stylised Byzantine manner and introduced a new realism, humanity and drama into painting. He also painted on the walls of the small Chapel of the Magdalen. Other 13th century masters worked at Assisi too, including Simone Martini and Pietro Lorenzetti, both Siennese, and probably the great Roman artist, Cavallini.

Later in the century, Assisi came under papal ban and went into decline. In the following centuries, various other artists worked there, but there were no major ones among them. Assisi's creative days were past. However, pilgrims continue to go there in large numbers to visit St Francis's tomb, and in 1968, the "World Day of Peace" was celebrated in Assisi. Invited by Pope John Paul II, representatives of almost all the religions met there for the first time in history and prayed for peace among peoples.

Assisi is not only a landmark for its art. It represents an entire stage in the emergence of Europe into independence and maturity, and the swing away from Byzantium back to the West. The new humanism had changed religion itself and gradually penetrated every area of life. It marks the waning of the Middle Ages and looks forward to the Renaissance.

European man had begun to stand on his own feet - and his feet are on the ground as they are in Giotto's paintings.

There was culture out there and we were out to get it. We had dedicated a day to charging through Umbrian art, from the National Gallery of Umbria in Perugia, to the Basilica of San Francesco in Assisi. The fact we'd been shaken out of our sleep by the first earthquake, at 2 a.m. on Friday morning, didn't stop us; there would be experts checking out the cracks in the Giottos, a friend told us, but that didn't stop us either.

We were in the post office in Perugia before noon when the second one struck. I wondered was I fainting, then realised the whole building was reeling backwards and forwards, then backwards and forwards again. There was a genteel panic, with office workers piling onto the streets and standing in doorways, but we weren't deflected. We had only one day and we were going to the gallery. "This is hardly the moment . . ." exploded one of the incredulous gallery staff at the door, while a more diplomatic one explained that they were shutting up for the day.

Churches shut, galleries shut. We were disgusted. But we headed on to Assisi anyway. When we asked the taxi driver was the basilica open, he told us he hardly thought so, as two or three people had been killed there that morning. Finally, silent about our disappointment with our day out, we joined a strange parody of a tourist trek, up to St Francis's basilica.

The last of the four bodies had been identified within the hour, when a mourner shouted out to his wife: "What shoes was he wearing?" Around this vacuum of horror stood a crowd of tourists, struggling to change the story of their day from one of cultural appreciation, to one of human tragedy.

Some just couldn't make the shift: "It just wasn't meant to be, Dad", one young American woman was saying, but he couldn't believe he wasn't getting into the basilica: "You're young enough to come back again, I'm not."

As controversy began to bubble as to why Umbria's environment department sent restorers in to consider the damage to the basilica when another earthquake threatened, this was the challenge for the tourists, myself included: to understand that the fact that the Giotto frescoes of Franciscan life would probably never be the same and that we would probably never now see the Fourteen Apostles by Cimabue and the inconclusively attributed Fourteen Doctors Of The Church was not a tragedy compared with the loss of the lives of the two restorers and the two monks killed as the frescoes crashed to the ground.