Theodore Gericault’s “Raft of the Medusa” (1819) is one of the most compelling and controversial images of its time. Painted on a vast canvas measuring about five metres high by seven metres wide, it used the scale and drama of history painting to portray a notorious, contemporary scandal.

It also broke with convention by emphasising individual suffering over public virtue, thereby anticipating the struggle between the Neo-Classic and Romantic movements.

The use of bitumen has left large parts of the painting barely legible today, but much of the force of the original can be gauged in a full-size copy made in 1859, currently on show in Tate Britain’s Constable to Delacroix exhibition.

Gericault’s painting was derived from descriptions of an infamous shipwreck that had occurred only three years previously in 1816. On July 2, the Medusa - a government frigate carrying 400 soldiers and settlers to the French colony of Senegal - ran aground off the coast of West Africa. The captain, senior officers and passengers commandeered the lifeboats, leaving 150 people to take their chances on a makeshift raft, hastily constructed out of the ship’s masts and beams. There was an agreement that the boats should tow the raft to the nearby shore, but within hours of the ship sinking, the connecting cables were cut and the men on board the raft were abandoned to the mercy of the strong currents and high seas. They had no means of navigation, little food or drink, and were so crowded on to the precarious vessel that movement was virtually impossible.

Days of horrendous suffering and deprivation followed. Many of the raft’s passengers fell overboard during storms while numerous others perished in a violent mutiny. From the third day the starving castaways were forced into cannibalism, and on day six the sick and mortally wounded were cast into the sea to conserve dwindling supplies. Fifteen hardy and desperate men managed to survive another week before finally being rescued. The ordeal lasted 13 days and 140 lives were lost.

Gericault was already keenly interested in scenes of brutality and violence, and when he read Correard and Savigny’s book he was immediately attracted to the raft as a subject that could make an unheroic age aware of the existence of extremes. Initially, however, he could not decide which episode to paint and worked on five scenes - the mutiny, cannibalism, the sighting, the hailing, and the rescue - before finally settling on the sighting as his theme. It is interesting, particularly given his Republican sympathies, that he did not choose to show the treachery of the Medusa’s captain or even the more obviously dramatic or pathetic subjects of the sailor’s mutiny or rescue. But the sighting arguably represents the survivors’ most terrible ordeal.

On the morning of the 13th day they spied a ship - The Argus - far off on the distant horizon. They spent half an hour trying to attract its attention, but the ship disappeared and they fell “from the delirium of joy, into profound despondency”. Gericault’s figures respond to the sighting in various ways. Some, past hope, turn their backs to the horizon.

Others stand and wait or pray for deliverance. The remainder, stirred to frantic activity, struggle to rise to their feet or mount barrels and signal to The Argus with billowing cloths. In a carefully constructed composition, the figures are fused together in a strong diagonal motion that culminates in the powerful torso of the gesticulating black castaway.

Yet there is no sense of relief or joy at the prospect of rescue, only a feeling of unbearable tension as the figures strain towards the distant ship that’s reduced to a tiny speck, barely visible on the horizon.

Rich, sombre colours, ranging from the grey and brown tints of flesh to the bruised green and purple tones of the sky, and strong chiaroscuro enhance the drama of the scene. Much of the power of the painting’s impact derives from the scale and proximity of the action. The foreground figures are nearly twice life-size and, together with the raft itself, are crowded close up to the picture plane. The immensity of the ocean is reduced to a narrow margin of sea and sky. As a result, the viewer is made to feel physically part of the action - as if he too is on board the raft - and to empathise strongly with the experiences of the shipwrecked men.

Gericault spent 18 months preparing his painting and famously immersed himself in every detail of the castaways’ ordeal. He compiled a dossier of descriptions and illustrations of the shipwreck, and commissioned a scale model of the raft from the ship’s carpenter. He went to Le Havre to make studies of storm-swept seas, and visited the Hopital Beaujon to study the appearance of the dying.

Most macabrely, he painted a series of highly realistic studies of the severed heads and dissected limbs that he kept in his studio so as to observe the process of bodily decay. The purpose of this research was to provide Gericault with insights into the shipwrecked men’s experiences and to ensure the authenticity of his work. Yet the painting is not a realistic or accurate portrayal of events. It does not show the raft or men as they would have appeared - emaciated, with matted hair and beards, their sunburnt bodies covered with sores and wounds. Instead, Gericault’s semi-nude figures have the healthy vigorous bodies of athletes. Borrowing elements from Michelangelo, Rubens, Pierre Guerin and A J Gros, he expunged all anecdotal detail from the scene, turning the sensation of the moment into a timeless monumental drama.

Joanna Banham is head of education at Tate Britain

Constable to Delacroix: British Art and the French Romantics is on show at Tate Britain until May 11. Teachers’ notes available on requestTickets: pound;8; concessions pound;6.50; school groups pound;3.50 per person Tel: 020 7887 8959 A one-day symposium on “Shipwreck in the Romantic Era” takes place on May 9 Tel: 020 7887 8062

Theodore Gericault 1791-1824

Born near Paris, Gericault received some training from Carle Vernet and Pierre Guerin, but was largely self-taught. His first major success was “The Charging Chasseur” (1812). He visited Florence and Rome in 1816-17 where he admired the work of Michelangelo and Baroque art. The “Raft of the Medusa” was exhibited at the Paris Salon in 1819 and then in London in 1820. After a stay in England from 1820 to 1822 Gericault painted and created lithographs of horses and jockeys. Among his last works are a series of portraits of psychotics. After a period of illness and depression, he died in Paris in 1824.

Lesson ideas

Key stage 2l Choose a figure on the raft and write or describe how you might feel at the sighting of The Argus.

* Try and estimate the distance of the raft from The Argus. How does Theodore Gericault convey nearness and distance here?

Key stages 2 and 3l Make a painting or colouring of the stormy sky on an overcast day. Key stage 3

* Discuss how realistic the figures are, then try and draw one of its occupants as they may actually have looked after many days without food or drink.

* Act out the trial of the captain of the Medusa, presenting the case for the defence and for the prosecution and calling on witnesses to describe events.

* Compare Gericault’s work with other paintings of disasters at sea. Which picture involves you most and why? Which picture gives the most space to the raging elements? How does this affect your responses to the work?

Key stage 4 * Gericault posed and painted each of his figures separately. Copy the poses in one of the main groups, then take photographs of each figure and try to put the photographs together in order to reassemble the group.

BooksNineteenth Century Art: A Critical History . Edited by Stephen Eisenman. Thames and Hudson, pound;19.96Constable to Delacroix. By P Noon Tate Publications, pound;29.99 Louvre website www.louvre.fr