Visions and poetry

The story of Griselda, the peasant girl whose beauty captivated the Marchese Gualtieri di Saluzzo, was painted on to three large wooden panels in the 15th century by an anonymous artist. Newly cleaned and now glowing' the pictures became the genesis of the National Gallery's major exhibition, Renaissance Siena: Art for a City.

The story goes: a nobleman out hunting on his white steed was bowled over by a fair maiden's beauty. Immediately he offers her marriage, but on one condition: that she shows him complete and utter obedience. Thus begins the tale of an exemplary wife from Boccaccio's Decameron (1348-51), painted around 1494 to mark the marriages of two sons of a wealthy Sienese family, the Spannocchi.

The tale continues in splendid detail with the Marchese constantly testing Griselda's obedience. After gaining her father's consent he publicly strips bare the blushing girl, redresses her in wedding finery and marries her. By the second panel he is kidnapping her newborn children, pretending to kill them, bogusly annulling the marriage and dispatching her. But this sorry tale of psychological torment ends with Griselda reunited in the third picture with her long-lost grown-up daughter who arrives in the guise of the Marchese's new bride-to-be. They all embrace, and presumably live happily ever after.

Little is known of the painter; he is simply called the Master of the Story of Griselda. But this seems appropriate for an exhibition that promises to tell the story of a lost Renaissance' by focusing on those unknown artists working within the volatile artistic, cultural and political contexts of late Renaissance Siena from 1460 to 1530.

Among about a hundred exhibits on show, including paintings, sculptures, drawings, manuscripts and ceramics, the names of four artists appear time and again: Francesco di Giorgio, Matteo di Giovanni, Neroccio de' Landi, and Domenico Beccafumi who as "the greatest of the Sienese 16th-century artists" claims curator Luke Syson (though why is difficult to see: his electric colours and strange soft figures are an acquired taste) has the last room all to himself. Yet none are well-known names, unlike their Sienese counterparts of a century and a half earlier - Duccio, Simone Martini, the Lorenzetti brothers - or their Florentine rivals such as Masaccio, Mantegna, Donatello and Michelangelo.

The art of Renaissance Siena has long been treated as poor cousin to that of its near neighbour, Florence. Textbooks say its golden age was over by 1400. This had much to do with Giorgio Vasari, an artist of the Florentine court, who published in 1550 one of the most enduring of Renaissance art histories that made clear that the cradle of the Renaissance was Florence. It was a view that set the tone for centuries.

But this is undeserved, Syson argues. Sienese artists of the late-15th and early-16th centuries produced work every bit as good as their rivals. It was just that it was different. And this difference was deliberate. While Florentine artists were perfecting naturalism and mathematically correct perspective, the Sienese were working within their own specific visual traditions: merging Renaissance classicism with medieval mysticism to express their city pride and identity.

Their art was visionary, poetic and exquisitely crafted, Syson says. "There's a sheer loveliness that runs through the show, a capacity to take you into another spiritual, ethereal realm." Take, for example, the life-size painted wooden statue of Saint Catherine, patron saint to Siena and Italy, made by Neroccio de' Landi in 1474. It shows a young woman dressed in Dominican habit who devoted her life to the sick and needy. Like the preacher Saint Bernardino, also in the exhibition, she was and still is a local hero in Siena.

Given that she is held in such high regard and that this, "their greatest icon", has never left Siena, it is amazing that they have allowed the statue to travel here at all. Normally standing in the oratory church in the Contrada dell'Oca, the District of the Goose (which incidentally won this year's Palio, Siena's famous horse-race), it is said to bless both district and the city itself. It is easy to see why it is so loved: it is quite simply beautiful, and the saint's veiled face has a distant, almost Byzantine look that has an astonishing depth of compassion.

Siena called itself The City of the Virgin,' a dedication thought to have originated in a vow on the eve of a victorious battle against the Florentine army in 1260. The Virgin was therefore one of Siena's most popular subjects and appears as heavenly protector' in, for instance, Sano di Pietro's 1456 The Virgin Recommends Siena to Pope Calixtus III, and in the city's unique Biccherne. These are account books with historical scenes painted on to their wooden or leather covers, and are extremely fragile. The ones here include scenes of the Virgin Mary protecting Siena from earthquakes and guiding "the Ship of the Republic" to calm waters.

One of the outstanding pieces here is Matteo di Giovanni's Assumption altarpiece from the Siena-ruled town of Asciano. You may already be familiar with the main panel from the National Gallery's permanent collection, but now for the first time it is reunited with all its surviving parts. There's a great deal about this painting that is typically Sienese: the generous gilding, sinuous lines and great disparities of scale, features that combine to give a shimmering golden grace to the central figure of the Virgin who rises up amid music-making angels. Meanwhile, Saints Michael and Augustine stand sentinel in the side panels.

It is a beautifully composed exhibition, running until January 13, and will give pleasure to anyone nostalgic for Italian art. But while it introduces us to artists largely written out of art history, I am happy to say it includes some of the better known too - Donatello, Pintoricchio of the virtuoso fresco cycle in Siena's cathedral, Raphael, Signorelli - who as visitors to Renaissance Siena produced wonderful art for a city.