What makes a masterpiece?

Five experts explore the genius behind some of the world's greatest works of art, from Sri Lanka's reclining Buddha to Caravaggio's momentous supper

The Birth of Venus

Alessandro Botticelli

By Paul Joannides, art historian

Botticelli's picture was almost certainly painted to celebrate a marriage. "The Birth of Venus" was a subject frequent in antique and, very occasionally, medieval art. But Botticelli's treatment is quite new and demonstrates a powerful visual intelligence. The painting's size demanded breadth and clarity. It is magical theatre: at the left, Zephyr and Chloris' conjoined silhouette is that of a looped-up canopy and the receptive cloak on the right doubles as a curtain withdrawn to reveal Venus' beauty. Botticelli's display, inspired by the curtaining of altarpieces, may, in turn, have prompted Raphael's exploitation of the motif in the Sistine Madonna, with its majestic vision of the cloud-borne Virgin.

Paler against pale, Botticelli's Venus floats against a high sky that seems a condensation of ether, rather than transparent. Her contours are slightly shadowed to make her stand out against the sky and the interior of her body lightened and unemphatically modelled to bring it forward. This was a principle absorbed by Michelangelo, who employed it in the central histories of the Sistine Chapel ceiling. It is a gamble saved from crudity only by draughtsmanly accomplishment: in Botticelli, as in Michelangelo, the intensity of the line, elastic and rhythmical, animates the figures and keeps the eye in constant exercise around them. Botticelli's "colour field" technique was also to affect Michelangelo: warm and cold colours are, as it were, cross-fertilised as the cool body of Venus is drawn towards the warmth of the cloak and the foliage.

Appropriately for a mythological scene, Botticelli drew on Classical sculpture, but it is well-known that the compositional structure is a transposed Baptism, with Zephyr and Chloris replacing angelic witnesses. It transfuses the meaning of baptism from the spiritual to the erotic: Venus is born from liquid as the soul is reborn in baptism. And since she sprang fully-grown from the severed genitals of Saturn, Venus' birth is divine. This explains another transposition, the equivalence of her face to those of Botticelli's immaculate Virgins.

Bewitching in her combination of beauty and freshness, the goddess looks shyly outwards, not yet conscious of her power. The Birth of Venus is sometimes interpreted as an evocation of the celestial (as opposed to the terrestrial) Venus, embodying divine rather than earthly love. But there is no reason to confine the painting to philosophy. Venus personifies physical beauty and modesty; if at the moment innocence reigns, physical love is perhaps imminent. The painting might be a bridegroom's vision on his wedding night. Botticelli and his studio executed at least two repetitions of Venus alone against a dark ground, the earliest example of a single mythological figure being extracted from a larger composition. This is the full-length close-up that follows the long-shot and it brings Venus into still more immediate relation to the viewer. She emerges modestly from shadow into the bedchamber – and the bridegroom's presence.

Paul Joannides is Professor of Art History at Cambridge University

The Villa of the Mysteries

Artist unknown

By Mary Beard, classicist

The most famous painting discovered in the buried city of Pompeii – indeed the most famous surviving anywhere in the Roman world – is the curious frieze that covers the walls of a large room in the Villa of the Mysteries, a substantial property just outside the boundary of the ancient city. Painted in the mid-1st century BC, its series of almost life-size figures, set against a luscious red background, has become the modern icon of Pompeii, copied on to thousands of posters, ashtrays and fridge magnets.

At one end of the room, opposite the main door, the first thing you would have seen as you walked in was Dionysus, sprawling semi-naked in the lap of his mother, Semele – or maybe his wife, Ariadne (the female figure only partly survives). This divine couple is clearly the centrepiece of the whole composition, with its exotic cast of characters. Leading up to the pair along the left-hand wall is a relatively stately procession: the naked child reads out words from a scroll; a woman carries a loaded tray, while looking out to catch the viewer's eye; a group of women cluster around some kind of container.

Yet, as the figures get nearer to Dionysus, things become decidedly stranger. Next to the figure of young Pan playing his pipes, his female partner (a "Panisca") appears to suckle a goat; a satyr, one of Dionysus' mythical followers, holds up a cup into which his friends gaze intently; at the corner of the room a woman seems to start back in horror – but at what?

The answer to that question is probably to be found on the other side of the divine couple. For here a woman kneels as she begins to reveal something beneath a dark cloth (a phallus, it is usually imagined), while the winged demon whips the bare back of a girl who buries her face in her companion's lap. Just next to her, a naked woman dances and plays the castanets.

What on earth is going on? And what kind of room was it that these images decorated? Perhaps, as the Villa's title has it, the frieze is meant to depict an initiation into the cult of Dionysus: hence the revelation of the phallus, and the flagellation. But the room is one of the showrooms of this large house, opening on to a portico with a panoramic sea view. So this would be a scene intended as an elegant backdrop to dining and entertainment. Others have preferred to see the painting as an allegory of marriage and the preparation for a wedding. The bride has been identified as a young woman shown seated to the right of the main door and the central couple. On this interpretation, Dionysus and his wife, Ariadne, would symbolise the divine nature of marriage.

The truth is that we do not know exactly what is depicted here. Indeed, part of the pleasure of the frieze is the way that it repeatedly plays with our ability to decode it. But there is a surprising sting in the tail. One reason for the impact of this frieze is the way that it envelops anyone who steps into the room. Another is the sheer lustre of the deep red background, against which the figures are set: "Pompeian red" at its loveliest. This colour, however, cannot entirely be attributed to the original artist. When the paintings were first uncovered, they were so badly affected by damp that unsightly salts leeched through the paintwork. In order to remove the salts, petroleum wax was carefully and repeatedly rubbed into the painted surface. That memorable sheen is, in other words, a 20th-century creation.

Mary Beard is Professor of Classics at Cambridge University

The Art of Painting

Johannes Vermeer

By Arthur K Wheelock Jr, curator

The Art of Painting holds a special place within Johannes Vermeer's oeuvre. While it displays all the captivating characteristics of his artistic genius – a carefully observed 17th-century Dutch interior illuminated by softly diffused light, exquisitely painted details, and a frozen moment imbued with psychological depth – it stands apart in its imposing scale and pronounced allegorical character. The painting must have had special meaning for the artist: he kept it in his possession from the late 1660s, when he painted it, until his death in 1675. And though he left his family in dire financial straits, Vermeer's widow still refused to sell it. Instead, identifying the work as The Art of Painting (De Schilderkunst), she transferred ownership to her mother to keep it out of the hands of creditors.

Vermeer's title indicates that he intended the picture to convey an abstract idea about the nature of painting. His concerns belonged to a long tradition in which artists and theorists had sought to define the fundamental characteristics of painting, and the significance they held for human understanding. Vermeer's interpretation of these intellectual ideas was innovative. He presented his allegory in the guise of an everyday scene, an artist painting a model dressed as Clio, the muse of history. Clio's crown of laurel denotes honour, glory and eternal life; her trumpet stands for fame, and the thick folio she clasps, perhaps a volume of Thucydides, symbolises history.

By placing the muse of history at the centre of his allegory, Vermeer stressed the importance of history to the visual arts. Seventeenth-century theorists argued that the noblest form of artistic expression was history painting, a term that encompassed biblical, mythological and historical subjects, as well as allegories. By creating such paintings, artists demonstrated their knowledge and originality of thought, qualities that raised painting to the elevated status of a liberal art. Indeed, in Vermeer's painting, the artist is not so much the recipient of the muse's inspiration as the agent through whom she takes on life and significance.

Vermeer enhanced the realism of his scene through his sophisticated knowledge of linear perspective, which he used to create a logical and convincing sense of space. Equally important was his masterful observation of light, as in the sunlight reflecting off the brass chandelier's polished surface – an effect he achieved with sure brushstrokes ranging from thick impastos of lead-tin yellow in the highlights to darker and thinner strokes of ochre in the shadows. Perhaps with an optical awareness stimulated by the camera obscura, Vermeer occasionally altered his painting techniques to create different pictorial effects. He softly modelled his paint, for example, to create the diffused appearance of the cloth hanging over the edge of the table, while he used broad, crisp strokes to render the bold image of the artist at his easel. Nevertheless, the thematic culmination of Vermeer's work exists not on the painting's surface, but beyond the curtain, where the full meaning of the allegory unfolds.

Arthur K Wheelock Jr is the curator of northern baroque painting at the National Gallery of Art, Maryland, USA

The Reclining Buddha

Artist unknown

By Antony Gormley, sculptor

This astonishing sculpture of the Buddha was carved in the mid-12th century at the great city of Polonnaruwa in central Sri Lanka during the reign of King Parakramabahu I. Some 14 metres long, the head alone measures almost two metres in diameter. Traditionally, the West has been resistant to the hyperbolic image, associating it with inflated egos and totalitarian monuments. However, colossal Buddhist iconography, from the great Buddhas of Bamiyan in Afghanistan and those of Luoyang in China, has always embraced scale to reinforce the public and collective nature of this philosophy of life.

The scale of the Polonnaruwa Buddha is monumental, but conveys a quiet joy and a sense of engagement and peace that has nothing to do with being dominant. There is an acceptance of the earthly in an image that is in, and of, the ground and is gently (and so differently from the greatest Western treatment of this subject, the four Pietàs by Michelangelo) returning to it.

The Buddha is carved from grey granite striated with white quartz lines. This striation suggests two quite different things: the "dream" of life that like a river passes through names and forms (namarupa), but also its very opposite: the reinforcement of material reality, palpable, perceivable and bounded by time and space.

The coexistence of image and landscape would be a brilliant conceptual proposition by itself, but to have realised it with such grace and formal purity is a miracle: literally an apparition in the real. Here is the abstract body of Buddhism – the body itself seen as a site. It succeeds by the acute tension between precept and a feeling for form inherent in this Indian-influenced approach to sculpture.

The treatment of vitality in mass is this work's most remarkable feature. The feeling of mass at rest is clear. The shape and size of a beached blue whale, there is a sense of a quiescent force in this object/place. Look at the extraordinary curvature of the left arm that lies like a sleeping snake on the upper thigh, exuding, like the whole sculpture, a sense of peace hard to reconcile with its size.

And what about the head and the expression it carries? The bird-winged eyebrows that echo the hovering smile and typically down-turned eyes that do not simply express samadhi (concentrated meditation), but the transition of consciousness in the final release of Nirvana.

What does the total image convey? The body is conscious but at rest, the formal relation between a carved horizontal plane and the multiplicity of curves, inscribed and volumetric. It conveys an acceptance of being over doing, but also the celebration of being itself.

The Supper at Emmaus

Caravaggio

BY Helen Langdon, art historian

The Supper at Emmaus was painted in 1601, at the height of Caravaggio's success in Rome. In his works, the stories of the Bible are given new and compelling urgency, for he sets them in the contemporary world. The disciples become travellers, with torn clothes and workmen's faces; martyrdoms take place in the dark Roman streets, where young swordsmen brawl and fight. His pictures have a strong feel of the studio. The cellar lighting enhances the three-dimensionality of the figures. It is this heightened realism, so evident in this painting, that is unique to Caravaggio's art.

The Supper at Emmaus shows the most dramatic moment in the story of Christ's appearance to the disciples after the Resurrection. Cleophas and an unnamed companion are journeying to Emmaus, and as they travel Christ draws close and walks with them. They do not recognise him, but he comforts them, and they invite him to stay with them at the inn. As they ate, "he took bread, and blessed it, and brake, and gave to them. And their eyes were opened, and they knew him: and he vanished out of their sight" (Luke 24: 30-31).

The subject was common in art, but Caravaggio has utterly transformed this muted story into an intense drama of sudden recognition. His aim is to involve the spectator, almost physically, and he uses a variety of devices to achieve this. A basket of fruit perches unsteadily on the edge of the table, as though inviting the viewer to move forward. The great gesture of the right-hand disciple, traditionally identified as Peter, seems to break through the picture plane, and echoes the swift perspective lines of the table – all of which lead to Christ. The still life explores the beauty of surface and texture, of cast shadows dark on the white cloth, of chunky, solid bread, and light passing through water.

Yet this is not an ordinary meal, but a moment of divine revelation, and it is the fall of unnaturally bright light that endows Christ with the radiance of a vision; this symbolic use of light is perhaps Caravaggio's most important innovation. Beardless and young, with a fleshy face, Jesus is not immediately recognisable, as he had not been to the disciples, and this adds to our sense of wonder at the resurrected Christ, restored to youth, and freed from suffering. He is framed by the shadow of the innkeeper, who, uncomprehending, stands still in darkness. Christ leans forward, but only for a moment – shortly, he will lean back into the shadows, and "vanish out of their sight".

Helen Langdon is the author of 'Caravaggio: A Life'

These are edited extracts from 'What Makes a Masterpiece? Encounters with Great Works of Art', edited by Christopher Dell (Thames & Hudson, £24.95,thamesandhudson.com)