I am standing in a tiny stone church at the monastery of St Serge in western Syria, surrounded by Byzantine icons that would take all my attention but for a woman trussed in scarves who is praying out loud.

The altar where she prays is a semicircular slab of marble, a remnant from the sacrificial altars of the pre-Christian world, and she is reciting the words in Aramaic, the ancient Semitic language of the Middle East, which almost disappeared during the Arab conquests.

Almost, but not quite. Sequestered in these stony hills in the Quallamoun Mountains, a pocket of Aramaic speakers remains, a link with the ancient world of the Old Testament.

If Jesus Christ was alive today, he could probably hold a conversation with this woman.

Syria is astonishing, an open-air museum of human history that constantly stops you dead in your tracks. Many of the prime movers of world history have swept through Syria at one time or another - Alexander the Great, the Emperor Hadrian, Saladin, Timurlane and Richard the Lionheart. Saul of Tarsus fell off his horse on his way to rout the Christians from Damascus, changed sides and as his alter ego - St Paul - helped change the course of the Roman Empire. Peel back the layers and you will find yourself at the very dawn of human civilisation.

To get to the 8th century Umayyad Mosque in Damascus, you must pass through a fortress that was begun by Saladin, walk along a covered bazaar built by the Ottomans, pass through a Roman gateway alongside the remaining columns of the Temple of Jupiter and finally arrive at the mosque, which was constructed on the foundations of an Orthodox basilica. And by the standards of Damascus, the Umayyad Mosque is a newcomer. As far back as the second millennium BC this was the site of a temple dedicated to Hadad, the Aramean god of rain and fertility. Damascus is the oldest continuously inhabited city on Earth. When the Romans built their temple here, half a dozen earlier civilisations had already left their mark.

Damascus' setting is modestly dramatic. It sits on a large and fertile oasis on the Ghouta plain, watered by the Barada River. To the east is desert, and showing their teeth to the west are the peaks of the Ante-Lebanon mountains, which are still covered with snow even when the almond trees are exploding into spring blossom on the plain below. For the traveller, whether the desert is behind you or before you, this is a natural resting place.

Damascus grew fat on the cargoes that passed along the Silk Road, and there are still shops in the souk that can sell you carved ivory from China or camel bags and lapis lazuli from Afghanistan. To the south-west of the Umayyad Mosque, several khans, the old walled caravanserais that were used as hotels by travelling merchants, survive as reminders of the city's mercantile days.

Its epicentre, both spiritually and socially, is the Umayyad Mosque. Entering the courtyard from the labyrinth that surrounds it, the courtyard of the mosque stretches before you in a yawning apron of white marble that is polished daily by thousands of stockinged feet, with a loggia on three sides and on the fourth, the mosaic facade of the central transept, casting a wavy reflection across the marble. The effect is dazzling, as it's meant to be. After Mecca, Medina and the Dome of the Rock, this is the holiest site in Islam - although this is only a shadow of the original, which was almost totally destroyed by fire in 1893.

Damascus though, for all its encrustation of aged majesty, does not fulfil the romance promised by its name. For the most part, modern Damascus is a study in socialist drab - the grey, concrete, utilitarian, falling-apart look that is the Soviet gift to world architecture. But this is only the exterior. Unlike the Western house, which looks outside, to the view, the Arab house turns its back to the world and looks inward for beauty, content and serenity.

Close to the Umayyad Mosque, the Azem Palace was the home of an 18th century Ottoman governor, a series of lavishly decorated rooms with painted ceilings and panelled walls built around a central courtyard with fountains and trees.

Just off Straight Street is another jewel box of a house, Beit Aqqad, which serves as The Danish Institute, with a courtyard paved with a geometric design in ochre, grey, white and honey coloured tiles; overlooking it, rooms are richly furnished with carpets and cushions, water pipes, spinning wheels and all the other apparatus of contented family life. Once seen, you begin to wonder what sweet pleasure palaces the grim, grey apartments of modern Damascus harbour.

Ditto for the women. Now and again a frisky breeze will lift their sombre cowls to reveal a coquettish hint of black stockings and a stiletto-heeled boot. And what about the astonishing abundance of racy lingerie shops, with their racks of faux-fur knickers and lacy black teddies?

When you come across a middle-aged woman in owlish glasses thoughtfully fingering a purple satin strapless bra in the Hamidiyeh souk, you realise that life behind closed doors in Syria probably has a certain zip to it. For the visitor's purposes, Syria is commonly divided into three main sites which form a triangle - Damascus, Aleppo and Palmyra.

Subtitled "The Bride of the Desert", Palmyra is a beauty, and the most fabulous of all Syria's many ruined cities. Its colonnades grope toward the sky like bleached whalebones, suggesting the splendour that once was, its temples stand serene and curiously naked amid the vast expanse of nothing that surrounds them, overlooked by an Arab fort that glowers menacingly from its hilltop.

Derived from the Greek word for the date palm, Palmyra is rescued from the desert by a spring, which feeds an oasis that dates back to Palaeolithic times.

Its glory days came during the second and third century AD, when Palmyra flourished as the most important of all Syria's caravan cities.

Politically, it maintained a nervy independence from the powerful empires around it, a buffer state between the Parthians and the Roman Empire, until its ambitious queen, Zenobia, finally challenged Rome itself and was brought to heel by the emperor Aurelian. As a Roman outpost it never regained its former wealth and importance, and over the following centuries Palmyra was swallowed up by the desert sands. Not until the late 17th century was Palmyra discovered by the wider world, and not until the 20th century did German and later French surveys reveal its riches.

Essentially Palmyra is long, narrow site with the Sanctuary of Bel at one end, Diocletian's Camp a kilometre away and between them, a colonnaded street with ruins scattered on either side. What remains is a skeleton. It takes real imagination to add flesh and blood to the foundations that were once the Baths of Zenobia or the Temple of Nebo - although the theatre is a small jewel.

These days the Bedouin have inherited the site, some of whom will give you their business card, complete with email address should you care to arrange a camel safari in the Syrian Desert.

An essential detour on the road between Palmyra and Aleppo is the fortress of Krak des Chevaliers, Qalat al-Huan in Arabic, "Castle of the Citadel". Krak is the perfect postcard fortress, the best preserved example of a crusader fort anywhere in the Middle East. In its sheer muscularity Krak underlines the powerful forces that have played out their set pieces against this backdrop. Built as an Arab fort on a much lesser scale, during the crusades Krak fell into the hands of the Hospitallers, the Knights of St Jerusalem.

Recruited from the flower of European nobility, the Knights evolved from a nursing fraternity which ministered to Christian pilgrims en route to the Holy Land into an elite corps of professional warriors - the Christian samurai in the holy war with Islam. Wealthy, educated, arrogant and devout, the Knights transformed Krak into a model of the military architect's science.

On a spur jutting from the mountains to the southwest, they built walls many metres thick, stables for several hundred horses and slotted ceilings where fire and boiling oil could be rained down upon the heads of an advancing enemy.

Saladin himself abandoned his siege of Krak after one single day, but ultimately, the Knights Hospitallers were stretched too thin in this hostile sea and after little more than a century of occupation, Krak fell to the Marmelukes, another caste of military, landholding, aristocrats.

Tucked into north-west Syria, close to the Turkish border, Aleppo is instantly likeable, and when a taxi driver refused to accept my fare from the old souk back to my hotel, I decided I liked it even better. Since time immemorial Aleppo has been a trading city, amenable to cultural influences from East and West, and a cosmopolitan flavour prevails, from its boutiques to its taste in outdoor cafes to the more liberal dress of its women.

Aleppo's historic flavour survives most vividly in the great bazaar, Souk al-Atarin, and sooner or later you must take your heart in your hands and plunge into its dark caverns. Inside is an Aladdin's Cave - every conceivable creation from the coppersmith, the butcher, the baker and the carpet weaver. One of the specialties is soap made from olive oil and sold in chunky brown blocks, and there are still functioning soap factories within the souk - as well as an ancient Jewish synagogue. The produce is arranged generically along narrow passageways. There's an alley full of twinkly gold bangles, a street of carpets and curved daggers, one dedicated exclusively to Bedouin tents and a coffee and a spice bazaar, where aniseed, paprika, figs, almonds and rosehip are raked into aromatic pyramids.

Just north of Aleppo, where limestone competes with green pastures for the landscape, there occurred one of the great flowerings of the Byzantine Church. Scattered across these rolling hills lie literally hundreds of what the Syrians call Lost Cities - extinct settlements that arose around churches and monasteries - and the most compelling of the lot is Qalat Samaan, St Simeon's, a fifth century church that even in its ruined state represents one of the architectural high water marks of the Byzantine style.

St Simeon Stylites was a fourth century monk who gained a reputation for extreme piety and asceticism. As his fame spread he removed himself from the world and spent the last 42 years of his life perched on a series of stone pillars, which gradually grew to the 18-metre pillar on this site. From here he would preach, attracting crowds of devotees and a cult of imitators, qualifying him as the world's first rock star.

It's a melancholy place, this hollowed-out church, frisked by a cold wind that comes straight off the peaks of the Kurd Dag across the Turkish border. If there's a lesson in these tumbled stones, it's the impermanence of things. Stone foundations have been torn apart by tree roots, arches frame empty blue sky, the carvings on the stonework have been softened by the elements and even St Simeon's pillar has been whittled down to a stump by souvenir collectors.

Echoing in my head was the memory of the Aramaic prayer from the Quallamoun Mountains, and so, having grabbed something worth hanging onto, I climbed into the bus and returned to the souk to buy an Isfahan rug.