I pinch the arch, but it is no daydream, but real - or rather a massive 30-by-15-metre whimsy of painted canvas. Executions in Morocco were customarily dispatched outside the principal gateways - but it is surely some macabre accident that this bank-sponsored construction stands over the site of the guillotine.
I cross myself and hurry along the last 500m to the exhibition, The Treasures of the Kingdom of Morocco, in the Petit Palais. Following a border of Saharan sand I am lost - in wonder and delight. From dusty museums across the length and breadth of the country, from otherwise inaccessible national deposits and close-guarded private collections come these totems of a 3,000-year artistic heritage. The prehistoric stone carving of N'Kheila etched over all the surfaces of a grey tablet is bewitching. The standing man, encircled by expanding concentric lines from three centres, is a representation of our position among the force-fields of spiritual life.
In Tangier the novelist Paul Bowles recognised the almost tangible currents of magic that criss-cross the landscape. From the mud layers beneath the Roman ruins at Banassa, beside the slow-moving waters of the Sebou, comes a golden flower medallion wrought by some Phoenician master-craftsmen. It speaks of Tyre and Carthage and their control of the secret trading routes that fetched tin from out of Cornwall and gold from West Africa.
The bronze of King Juba II is the most beautiful Roman portrait to have survived from antiquity. Recognisably north African, Juba also belongs to the wider Mediterranean world. Carried through the streets of Rome as an infant during Caesar's triumph, this orphan of the royal house of Numidia was later brought up in the household of Augustus. The bust was probably made at the time of his betrothal to Cleopatra Selene, daughter of Mark Anthony and Cleopatra.
Calligraphy was ever the first of the Islamic arts. Its disturbing power can be felt even by the illiterate in an open folio of prayers composed by the Sufi master al-Jazouli. This extraordinary encapsulation of the power of the word with its massive dark shadows and attenuated line is executed in the traditional Maghribi script.
By contrast, the portable arts, especially the glittering displays of draped textiles and hung jewellery, speak of the ancient traditions of Persia and Byzantium rather than Mecca. The endless duality of the Moroccan countryside versus the Moorish city is everywhere to be seen: silver versus gold, geometric rather than floral, earth colours contrasting with rich pigments, weaving with embroidery. The show closes with tributes from Morocco's recent admirers - some sketches of Tangier by Matisse and Raoul Dufy - and is dominated Van Dongen's portrait of a young Arab boy. A final lingering exit is made past Bruno Barbey's contemporary photographs which remind us that romance, mystery and spiritual quests are not just made in the past.
The Treasures of the Kingdom of Morocco. To 18 July, Tue-Sun from 10 to 5.40, Petit Palais, Avenue Winston Churchill, 75008 Paris (00331 42 65 12 73)Reuse content