But push open the creaking wooden doors and tragedy lies within: hundreds of delicate 800-year-old frescoes depicting the entire Biblical epic, flaking from the walls, glistening with condensation and damp. Another Lebanese disaster.

St George and St Theodore ride in triumph along mouldering walls – the Maronite and Orthodox Christians preferred bellicose heroes once the Muslim warriors of the Prophet had arrived in the Levant. Yet staring from the inner darkness of apses and the pre-Christian Roman walls which protect the original buildings are Jesus and Joseph and Mary and the Archangel Gabriel and, of course, a winged Satan and Moses. Sometimes the fading texts are in Syriac, sometimes in Latin or Greek.

In Europe, there would be a heritage society to restore these treasures. Alas, in Lebanon these past 25 years, amateurs have tried to protect ancient art with coarse, comic-cut results. In all, the frescoes of 20 churches are now in danger.

Christian Décobert of the Paris Ecole des Hautes Etudes en Sciences Sociales points to the head of Moses in the church of Bahdeidat with its semicircular roof. The holder of the Ten Commandments looks out at believers with big revelatory eyes, his eyebrows almost as black as his beard. “The artists used to go from church to church – and paint the same faces,” he says. “All the faces on these walls are the same.”

And he’s right. When I step into the church at Ma’ad, an identical Moses greets me behind the altar, the same beseeching eyes, the same sense of wonderment in his expression. I suppose you would call it “school of Moses”. It might take a day to walk from one village – and source of income – to the next, but the result was the same. Identical saintly reproductions can be found in Coptic churches in Egypt.

Levon Nordiguian, chairman of Lebanon’s Musée de Préhistoire, stops before a garish, over-red painting of the Apostles, the fruits of an over-zealous – perhaps over-religious – worshipper, and shakes his head with a mixture of astonishment and horror. Where the amateurs have tried to replace the ancient frescoes, there can probably be no restoration. “Whoever did this thought he was rescuing his religion,” he says. “For me, he was destroying his heritage.”

Frescoes have a mesmeric quality about them. There is no sense of perspective – the Renaissance has not touched these Crusader churches, though some were constructed in Mamluke times (1250-1517) – and the faces, those that survive, have a peculiar innocence about them, relics of a time when faith was unchallenged within the Christian community. The story of the Bible had to be explained easily in an age when a far more powerful religion was cloaking the Holy Land. Many of the churches are supported by original Roman columns.

Two hundred miles to the south of these churches, Jerusalem was lost to Saladin in 1187 – the city was surrendered by Balian of Ibelin, as every viewer of Ridley Scott’s filmKingdom of Heaven will remember – and the Crusaders were confined to city states on the coast. The nearest to Ma’ad and Bahdeidat was Tripoli, 30 miles up the coast, but it could have afforded little protection. The frescoes were there to do that. Hence St George and St Theodore and their heavily armoured horses on the walls.

In many cases, the eyes of the saints and holy men of Christianity have been gouged out, and local Maronite villagers tell visitors that this was the work of the Muslim invaders. Untrue, say the experts. Many monasteries converted to Islam and the monks themselves cut the eyes from their own Biblical heroes in order to conform to the Muslim world’s refusal to countenance the portrayal of a human face in a place of worship.

Some of the characters in the frescoes – with or without eyes – are as local as the villagers. St Charbel of Edessa and his sister, Barbaria, for example, are Lebanese icons – Charbel still reputedly weeps from an uncorrupted body in his Lebanese tomb – and there are a series of quite unknown figures, men and women, who hover in supplication beneath the Holy Ghost and God himself; these are the donors, those who wished to ensure their place in the afterlife – and in the local early Christian societies of this region – by paying the wages of the fresco painters. We will never know their names, only their likenesses, the ages of the men betrayed only by the whiteness of their hair.

M. Decobert pads down to a second church in Bahdeidat, built, it seems, on an earlier construction; a Greek inscription on a cornerstone stands upside down beside the door. “My theory,” he says, “is that when the Arabs arrived in Egypt, the Near East and in north Africa, all these countries were Christian. Half of the Persians were Christian. At that time, the social system in the Byzantine Empire was founded on the monasteries. It was not at all like the Roman system where the cities were the centre of economic decision-making. Under the Byzantines, there was a man of religion who had power and very frequently he was in charge of the collection of taxes. Monasteries were somewhere between the places of production and the purchase of these products. Caravans, boats, militias, they were all privately owned in the Byzantine system.”

But at the end of the 8th century, when the Arabs began to settle into their newly conquered lands, they decided to create an administration. “Some monasteries disappeared. Some survived. Some converted to Islam – this was nothing to do with faith, it was about the cultural system. And the first people who converted to Islam were the monks. So the heads of the monasteries became key people in the Islamic system. There was no distinction between religious and economic life.”

So it is this era of history – the critical moment when the power of Christianity in the lands of its origin passed to Islam – that is now being lost forever in the stepped hills of Lebanon. In all, the frescoes of 20 churches – 10 Maronite and 10 Greek Orthodox – are endangered or already decaying, in Jbeil [Byblos], Batroun, the Qoura district of Lebanon and the Qadisha gorge, where ancient caves provide proof of the original Christian refugees who fled from the Orontes river valley into these inaccessible fastnesses. Lebanon’s last hermit lives here, maintaining his archives in a cave, nursing his old degree from the University of Louvain.

In response to this cultural crisis, a group of Lebanese academics and ecclesiastics have formed the Association for the Restoration and Study of Lebanon’s Medieval Frescoes. The co-ordinator is Dr Ray Mouawad of St Joseph’s University in Beirut (e-mail: rayjom@inco.com.lb) who specialises in medieval studies. “The frescoes are of great historical and artistic value, not only for Lebanon but for the whole context of Middle Eastern Christian art,” she argues. “They are in an advanced state of decay due to harsh climatic conditions – rain, humidity, excessive heat – or to human depredations like graffiti and ‘renovations’. They need qualified teams of restorers, who cannot be found in Lebanon, to take the measures that will help to preserve them.”

Dr Moawad’s project aims to organise the financing of these teams and to encourage tourism to the restored sites and bring money to the often impoverished villages in which the churches stand. Already the association has raised $24,000 of the $124,000 (£67,000) needed to restore the frescoes in two churches at Kfar Shliman and Kfar Hilda but they say they need at least another $1m for the remaining 18 churches.

The frescoes and the churches themselves explain the cultural history of the time, for they are not just relics of faith but symbols of economic power. A village – however small – which could boast three churches was displaying what we might today call “conspicuous consumption”, a display of wealth to rival and embarrass neighbouring hamlets which were poorer.

Yet still the frescoes light up the interior of these warm, dark churches, stained by candlelight and damp as they are. At Bahdeidat, the peeling designs are in a funeral room with walls that were part of a Roman temple. The face of the Virgin has disappeared but there are mitred bishops and a host of angels preparing to carry a saint to heaven, along – I fear – with what appears to be an anti-Semitic image of a Jewish figure under accusation for the killing of Christ. One donor appears in a brown robe, eyes raised to heaven, black-bearded; another is a young woman. But much of the centre of this fresco is a mass of black, of rotten, bare wall and of heavily stained paint secured by an old screen of silk – the pathetic remains of an earlier attempt at restoration.

And unless work starts soon to rescue this testimony of Christian history, these frescoes will have a future no less bleak than the Crusaders who once worshipped here; a memory of a lost faith, fading as fast as the continuing exodus of Christians from Egypt, Iraq, Lebanon, from “Palestine” and Syria and all the lands of the Middle East.