What should we make of the Pinturas Negras? The bleak ravings of a madman, a deliberate if cynical experiment in inculcating terror, or a calculated warning to humanity? All three explanations, and many more besides, have been postulated by scholars.

Anyone who has visited the modern-day Museo del Prado in Madrid does not need to be told how disturbing Goya's Black Paintings are. We can only imagine the feelings they must have induced in their original setting of the Deaf Man's Farmhouse, among God-fearing men of the painter's own time.

The dog in the yard outside began to bark. Carlos Olivarez da Salinas drew the watch from his pocket, inspected it and scowled. Turning in his seat, he peered through the rain-speckled pane into the gloom beyond. This had to be his visitor, and about time too. The realtor from the city had kept him waiting all afternoon at the little pension on the shore of the Manzanares River.

Moments later, a man burst through the door, his hair plastered to his forehead and his coat tails spattered with mud. 'Alejandro Rojas Enriquez at your service', he declared, with far too much enthusiasm for someone in such a bedraggled condition. 'Sorry I'm a bit late. We'd best get going straight away. We can take the gig outside, if the road's all right. What do you think?'

For Olivarez, all thoughts of a polite reception had drained away hours ago. He remained in his seat, and stared impassively at the young man for what he hoped was a disconcertingly long time. 'Hang that coat by the fire', he said eventually. 'It's too late to go anywhere tonight'.

The visitor looked crestfallen. 'Are you sure?' he asked. 'I only need to make a quick inspection. If we do it now, I could head back to Madrid at first light'.

'It's October', Olivarez replied, making no attempt to disguise his annoyance. 'It'll be dark in half an hour'.

'I could see what I need to see by a lantern', said the young man hopefully.

Olivarez snorted. 'Trust me', he said, a smile on his face for the first time. 'You do not want to be up close to those pictures in anything less than full daylight'.

Rojas sighed and waved to the carter through the still open door, before pulling it closed. He clambered out of his coat and draped it over the iron rack at the fireside.

'Good choice', said Olivarez, evenly. 'Now, I've been four hours without a proper drink waiting for you to show up. And in a posada, no less. Get me some brandy'.

Francisco de Goya y Lucientes was a Madrileño only by adoption. The son of a master gilder, his birthplace was the village of Fuendetodos near Zaragoza. His father's patrons helped the young Goya to find an apprenticeship in Madrid, where he studied under Francisco Bayeu, a court painter whose sister he would later marry. The pupil was both accomplished and well-connected. By 1772, he had secured an appointment in the court of Carlos III.

Goya was a rebel from the beginning, but in these early years the trait manifested itself only in his bohemian behaviour. His paintings were models of artistic convention, and he executed work in the style of the masters such a Velasquez with elan. For a long time, it never occurred to him to do anything else. This was the kind of work that an up-and-coming painter was paid to do, and paid handsomely too. For a hedonistic young man surrounded by opportunity and temptation, that's all there was to it.

Alejandro Rojas Enriquez mopped the last of the stew from his dish, and poured out some more of the brandy for them both. By now it was dark outside, and if anything the weather was worsening, making the other man's reluctance to go up to the house seem a little less unreasonable. Nonetheless, Olivarez was obviously a typical provincial, his intransigence founded in resentment of a self-made young man from the city. There couldn't possibly be any substance in his ominous remarks about the pictures.

Rojas mulled over what his employer had said. Their client was a wealthy French banker, one Emile d'Erlanger. He was minded to buy the house on the recommendation of some academic or other, purely because of the paintings. Rojas had been confused at first. Why would you have to buy a house to obtain a few pictures? Then he discovered that they weren't hanging on the walls. Instead, they'd been applied straight onto the plaster, and in oils too. d'Erlanger had had photographs of them taken, and now his decision to purchase rested solely on the feasibility of the paintings' removal. Price was no object. In fact, the offer price suggested would probably be enough to buy the whole parroquia.

Anyway, there was still work to do that night. Rojas chinked his glass against the other man's, and switched on his easy smile. 'So, Senor Olivarez da Salinas, are you going to tell me about la Quinta del Sordo?'

The last of Spain's old masters was destined also to be the first of her great modern painters, since Goya increased in daring as his prowess grew. The better off he became, the less respect he was obliged to pay to the social mores of his betters. He found patrons of like spirit, such as the Duchess of Alba, and there were paintings that caused great controversy such as the paired portraits of the Maja, one clothed and one naked.

And yet this was a trivial controversy compared with what the painter saw. His outlook began to change after 1793, when an undiagnosed illness (possibly polio) left him incapacitated for several months. After the spasms relented, Goya found himself permanently and profoundly deaf.

Spain was sick too, and Europe was racked by war and political expediency, and the lately-chastened Goya observed it all with a new found clarity. His work took on a journalistic quality, and his paintings became ever less mannered. He represented his subjects warts and all, and some of them were merely ugly, and some became images of depravity and despair.

Olivarez shrugged. 'It's just a farmhouse. It's about two miles further south along the river, on this bank. It stands a few yards down a track, away from the main road. It has two floors, and a little wash-house alongside. That's all, really. Except for the paintings'.

Rojas refused to be subdued by the other man's reticence. 'The Deaf Man's Farmhouse. Because Goya was deaf, right?'

'Wrong. The deaf man was the previous occupant; a coincidence. Nobody knew Goya was deaf. In fact, nobody knew him at all. He was pretty well a recluse the whole time he lived there'.

'So why did he come here? What was wrong with his place in the city?'

Olivarez stared blankly for a few seconds, and Rojas charged the glasses again and looked bright and expectant. The stolid dialogue continued.

'He had a mistress, and his usual clientele didn't approve of her. He probably couldn't afford the town-house any more either, because he'd p*ssed everyone off and wasn't getting enough work. He bought the farmhouse early in 1819, already well into his seventies. He stayed four years, and then he just walked out one autumn day almost exactly fifty years ago. He left the place to his grandson, and that was it for Goya and Spain. They say he went to Bordeaux'.

There was a silence. Rojas didn't know why he felt such trepidation, but he said it all the same.

'And what about the paintings?' asked the realtor.

Spain was dwindling in those days, her time of conquest long past, and now a tyrant to the east, Napoleon Bonaparte, was a perpetual threat. In spite of a series of demeaning treaties, the French garrisoned Castile much as they pleased. The populace despised them, and things came to a head in the Spring of 1808. A cavalry unit was sent to quell a riot in central Madrid, and found itself set upon and put to humiliating flight. The very next day, May 3rd, the French took their revenge. Partisans and innocent bystanders alike were herded into a city square, where they were callously shot down.

It may not have been the first atrocity to which Goya bore witness, since he lived in particularly violent times. It may not even have been the first occasion on which pity for his persecuted brethren boiled over into rage. It was to be the first time, though, that he poured his emotions onto the canvas. His oeuvre changed almost overnight. The rake who loved to titillate and startle his audience was now committed to an entirely different kind of shock. Goya resolved to show humanity the consequences of its evil in unflinching, graphic detail.

Art as a political instrument was changed forever at the beginning of the nineteenth century. Until that time, it was a pacifying influence, manipulated by the powerful. Now, if anyone could control it at all, it became a call to arms.

Olivarez hesitated at the question. This time, it was clear that his slowness to answer came from troubling thoughts.

'There are fourteen paintings', he said finally. 'I don't remember any of them very clearly, and I like it that way. All but one of them scare me sh*tless, if I'm honest. They'd scare anybody, but they're remarkable. It's criminal that they've been left to rot. The authorities should have preserved them years ago. Either that, or burned the place to the ground and begged for mercy'.

Rojas was perplexed. The young man was enjoying his last day of innocence. Not until the following morning would he comprehend that mere paintings could command such awe.

The realtor opted for safety. 'Tell me about the one that doesn't scare you', he suggested

'It's a dog', Olivarez smiled. 'Only it's composition is all wrong. It's looking over the edge of a sand-dune or something. You can only see its head, and a hell of a lot of sand'.

Goya's Dog was on the second floor of the Quinta, where the paintings were more damaged, both through exposure to the elements and in their disintegration during removal.

The painting is a modern icon. Its layout is masterful to today's eyes, but it must have looked absurd in contrast to classical conventions. The dog itself seems as abject and lonely as only a dog can.

'I think he meant something by the sand'. Olivarez was almost whispering now, as if threatened by unseen listeners. 'Some of the others had sand. There are two peasants stuck in quicksand, beating the sh*t out of each other with clubs. They're going to die anyway, and it seems that the last thing they've chosen to do in life is to hurt someone else. Then there's a weird rock in the desert with witches flying round it'.

These two paintings are sometimes called 'the Cudgels' and 'Asmodei'. Both were probably on the ground floor. The witch theme appears repeatedly throughout the paintings of the Quinta. There is one depicting the Fates. As in Asmodei, they levitate disconcertingly. There is another one of two crones eating, one of them with horribly skull-like features, that recalls Macbeth. Three more paintings show a pair of monks, men poring over a book, and men and women carousing. All are in deep shadow. The leering faces of several of the characters convey a sense of cruelty and debauchery. A further painting shows Judith, her knife poised to hack at the neck of Holofornes. Then there is an image, Maja-like, of Goya's mistress Leocadia. At first impression it is lighter than the others, but what seemed to be a bedhead turns out on closer inspection to be a tomb-rail, and the temptress in the boudoir is transformed into a widow at the graveside.

'There's another witch painting', continued Olivarez, subdued. He seemed to avoid Rojas' eyes and his hushed voice was almost inaudible above the cackle of the rain on the tiles above their heads.

'It's a coven. The Devil is there, completely in shadow and in the shape of a huge horned goat. All the witches are entranced. They have horrible pin-prick eyes and hollow faces. There's just one girl, at the edge of the group, who appears normal. She's being initiated. They're going to possess her too'.

The largest single painting of the fourteen occupied one whole wall of the ground floor room of the Quinta, and is over four metres from side to side. It was originally even longer than that: the restorer truncated the right hand end, presumably because it was irreparably damaged or lost.

This is the end where the girl sits. She too wears Maja-like mourning clothes, and her face is partly obscured. Her isolation counterpoints the seething crowd that makes up the rest of the painting. Her innocence accentuates the evil of the others.

Rojas counted on his fingers. 'I think you've mentioned eleven', he concluded. 'They do sound fairly nasty, I'll grant you. You haven't persuaded me that they were unsuitable for evening viewing, though'.

The other man shuddered. There was another long pause before he spoke. 'Two of the remaining ones are of pilgrims on the road to San Isidro. One of them is not too bad, just dark and brooding. But the other one...the people's faces in it...you would not want to see them by candlelight'.

The Pilgrimage to San Isidro is an important theme in Goya's work, because he painted it many times, with a notable example nearly fifty years older than the terrible painting from the Quinta.

This early depiction is colourful and optimistic. If the young Goya intended a noble, pious quality, he slipped instead into a pastoral fantasy. The outcome is facile and inconsequential.

The darker of the two Black Paintings is a shocking antithesis of the youthful version. The contorted faces of the pilgrims seem to draw the observer in, since the only light in the picture is the ring of pale of flesh surrounding howling wide-open mouths. There is no hint of spiritual salvation about the work. In its place we are shown torment, possession and corruption. The onlooker is left in no doubt about Goya's contempt for a Church of Man sundered from God.

Olivarez now fell completely silent, intent on the table top.

Rojas could feel the hairs on the back of his neck standing upright. The question came out of him without any conscious intent. His mouth was almost too dry to voice it.

'And the last?'

Olivarez said nothing. He slowly raised his head and stared blankly at Rojas. The look on his face made the young man start in his chair.

Very few subjects of classical myth were shunned by the painters of the royal courts of Europe. The most lurid of stories, conventionally treated, could be dignified by a formal setting. At the same time, the most popular themes retained the surreptitious thrill of forbidden cravings. There was one legend, though, that seems to have conjured images too extreme for even the most perverted of patrons.

Rubens was the only major painter before Goya to tackle the variant of the Saturn-myth in which the deity eats his own children. The Flemish master's work of 1636 looks banal nowadays, like an oddly-dressed grandfather blowing a raspberry on an infant's tummy.

Goya's version of the tale is arguably the most gruesome painting ever to win major acclaim. There are several stark differences from the Rubens treatment, not least the conspicuous madness of the God, gnawing goggle-eyed at the bloody torso of his child. The victim has adult proportions and an indeterminate gender, and nothing at all is left to the imagination. The original, indeed, had an erect penis, but either Goya himself or more likely a prudish restorer painted it out.

Numerous interpretations have been put on the painting, none of them comfortable. In the context of Goya's general work, it may well refer to the madness of Spain itself, and the massacre of the nation's children in the pursuit of crazed and blood-soaked war. At the same time, though, just about any of mankind's gravest sins can be ascribed to it. It induces contrition as well as horror.

Alejandro Rojas Enriquez carefully folded his britches. He sat down on the edge of the cot instead of climbing into it, and watched the candle-flame for minutes on end. Finally he stretched out on top of the sheets with the light still burning, and waited for dawn.