Figure holding a San Pedro cactus, Chavín, c. 1200 BCE.

In the opening paragraph of The Doors of Perception Aldous Huxley traced the story of mescaline back to the peyote cactus, ‘a friend of immemorially long standing’ to ‘primitive religion and the Indians of Mexico and the American Southwest’.1 But some scholars already suspected by that point that mescaline also had another ancient source, one attested in art, sculpture and architecture dating back hundreds of years further than the Spanish chronicles that offer the first cultural records of peyote. In 1947 the Peruvian pharmacologists Carlos Gutiérrez-Noriega and Guillermo Cruz-Sánchez published the first of a series of papers that tentatively identified the presence of mescaline salts in the family of tall columnar cacti known across the Andes in Spanish as San Pedro and in Quechua and Aymara as achuma or huachuma. In 1950 they documented its secret use on the Peruvian coast in traditional healing ceremonies that were still prohibited under laws against sorcery, and in 1959 the presence of mescaline was confirmed in Trichocereus pachanoi, the classic San Pedro.²

This identification dovetailed with recent discoveries made by the Peruvian archaeologist Julio Tello, who had been excavating since the 1930s at the mysterious temple site of Chavín de Huántar in the snow-capped range of the Cordillera Blanca in the high Andes. The temple structures at Chavín – a huge complex of sunken plazas and step pyramids, with evidence only of minor habitation and no trace of military fortifications – are surrounded by massive walls of faced stone blocks studded with elaborately carved heads, some up to half a ton in weight, held in defiance of gravity by concealed tenons. The heads are part human and part monstrous feline, with exaggerated jaws and fangs. Many are contorted and grimacing, and some have streams of mucus flowing from their nostrils. The oldest of the sunken plazas, dated to at least 1200 BCE, has a frieze running around its circular inner wall at knee height featuring a similar figure, snake-haired, sprouting fangs and claws and clutching an unmistakable San Pedro cactus.

Chavín had previously been assumed to be a far outpost of some Mesoamerican civilisation, perhaps Olmec or Maya, but a landslide in 1925 that altered the course of the Mosna river above which it perches enabled Tello to recover potsherds that pushed back the date of its habitation and revealed a three-stage construction spanning close to a thousand years. In the twisting network of subterranean chamber-galleries under the old temple he focused his attention on a carved stone stela (which he named the Lanzón for its lance-shape), its surface carved with a fanged humanoid figure that he identified with the deity Viracocha, later worshipped in a different form by the Inca. By the time of his death in 1947, just as the presence of mescaline in San Pedro was being revealed, Julio Tello had won acceptance for his theory that Chavín was far more ancient than previously assumed and represented a previously unsuspected pristine culture of monumental architecture in the Andes.

The evidence for this culture, now named Chavín or Early Horizon, has grown considerably in the interim, particularly since 1994 when Ruth Shady Solís of Peru’s National Archaeological Museum began work on a complex of sites in the arid coastal valley of the Norte Chico around a hundred miles north of Lima. This barren desert, where rain never falls except in El Niño years, is dotted with huge mounds which were assumed to be natural formations but turned out to be complexes of plazas and pyramids, some older than any in Egypt. Like Chavín they appear to be ceremonial: they stand unfortified, situated away from the irrigated streams of snowmelt in the valley’s heart, and appear to have been inhabited only by a small number of priestly functionaries. Caral, the first to be excavated, is now dated to 2700 BCE, and some of its neighbouring structures may be even older.

These coastal complexes are connected to Chavín not only by their monumental architecture but by imagery – depictions of tropical birds and monkeys, native to the highlands, decorate bone flutes found there – and by networks of trade. On the barren coast, in the permanent sea-mist that clings where the desert heat meets the cold Humboldt current, waste middens dating back millennia are exceptionally well preserved. They reveal a material culture founded on fishing the rich Pacific coast with cotton nets and gourd floats, technology that allowed a sizeable population to thrive in the harsh landscape. They also include objects that must have been sourced from the distant mountains and beyond including, alongside the pyramid complex of Las Aldas, the preserved skins of cacti, presumed to be San Pedro, rolled neatly like cigars.3

The switchback road up into the Andes gives a sense of the organisation and energy that the trade route would have demanded. The baked silt and pebble crust of the coastal plain stretches for miles inland without shade or water before the foothills begin to rise. The slopes are gradually colonised by scrub and bushes until, at an elevation of around 1,000 metres, the clouds forced upward by the desert heat coalesce and clothe the slopes in green. The arable land between the scree slopes becomes a patchwork of small farms growing subtropical fruit – guava, lime and lucuma – and stands of coffee and coca bushes beneath the shade of avocado trees.

At around 2,000 metres the air thins, the lush foliage dies away and the domain of the San Pedro begins. The cactus clings to the high, barren cliffs, sometimes as a single stem but often in clusters that fan upwards like organ pipes or collapse under their own weight and trail like cucumbers down the gravel slopes. For three months of the year they are wreathed in hanging cloud and drizzle; for the other nine they are blasted by the high tropical sun. Their skin colour ranges from a parched olive green to a rich emerald, often dusted with a delicate verdigris bloom that rubs off at the slightest touch and takes months to re-form. In the spring they flower magnificently, a dazzling explosion of life from a dull and apparently lifeless stem, usually a single bloom that unfurls from near the top. The flower is a luxurious frill of creamy white and yellow petals that opens at night with a lemony scent and is pollinated by hummingbirds and bats.

This is the ancestral domain of the cactus. The family evolved in the desert regions of South America some 30 to 40 million years ago, long before the southern continent became joined to the north. Cacti are part of a unique flora and fauna – sloths, tapirs, anteaters, llamas, vampire bats – that developed idiosyncratically in this self-contained world. Under the fierce sun they selected for ever smaller leaves and for thicker, leathery skin. To avoid losing moisture they opened the stomata that collect carbon dioxide for photosynthesis by night (rather than by day, as do other plants). During the day they synthesise their sugars, and San Pedro is usually harvested in the late afternoon when at its sweetest. The first cacti developed areoles, a unique feature from which their spines – modified leaves – emerge. Their stems became receptacles that could swell to hold huge volumes of water within their dusty and wrinkled exteriors, in the form of thick and often bitter mucus.

Why the San Pedro and peyote cacti should contain mescaline is a mystery – or, more precisely, a cluster of interlocking mysteries. Mescaline seems to occur in nature only within the cacti, and within the cacti only significantly in two families that are about as distantly related as it is possible for cacti to be.4 Recent studies have identified it in a growing number of species, but mostly within the Trichocereus and Echinopsis genera, closely related to the San Pedro and usually present only in trace amounts.⁵

In outline the biochemistry is well understood. Mescaline is one product among many of the conversion by methylation or hydroxylation of the amino acids tyrosine and phenylalanine, which are widespread across the plant and animal kingdoms – present in the human body, and in many of our foods, such as meat, eggs and milk. It is an alkaloid, a type of compound commonly produced in plants from the building blocks of amino acids. The term ‘alkaloid’ derives from ‘vegetable alkali’, coined by the German chemist Friedrich Sertürner, who isolated the first of them – morphine, from the opium poppy – in the early nineteenth century. He had expected that the pure chemical would be acidic, but it turned out to be an alkaline salt. Over 7,000 alkaloids are known, and San Pedro and peyote both contain around fifty others beside mescaline.

The more difficult question, and presumably the key to unlocking the mysteries, is what purpose these alkaloids serve as far as the plant is concerned. Most alkaloids contain nitrogen, often in the structure of a benzene ring, and it was assumed for a long time that they were metabolic by-products whose purpose was to flush excess nitrates out of plants, the equivalent of animal waste chemicals such as urea. The picture now appears considerably more complex. Alkaloid levels in plants rise and fall during their diurnal cycles, suggesting they have a metabolic function. They are often shuttled from the sites where they are produced to other parts, such as leaves or roots, and between different types of cells. Some plants contain them but others, often closely related species, do not. Their overall distribution across the plant kingdom is without obvious pattern. Some studies suggest that they are unusually prevalent among the cacti, but there is a wide discrepancy between estimates.6

Mescaline, one of many plant alkaloids that are psychoactive in humans (like opium in poppies, caffeine in tea and coffee, and psilocybin in magic mushrooms), belongs to a chemical family known as the phenethylamines, which are readily synthesised from the amino acid phenylalanine (this is reflected in mescaline’s full chemical name, 3,4,5-trimethoxyphenylethylamine). In this respect mescaline is different from the other compounds regarded as classic psychedelics – LSD, psilocybin and DMT – which are not phenethylamines but tryptamines, another family of alkaloids more similar in structure to the amino acid tryptophan. All share the same basic mechanism of action in the brain – binding to and activating the serotonin or 5-HT receptors – but, whereas the tryptamines’ most pronounced alterations are cerebral, mescaline generates a wider spectrum of sensory and physical effects.⁷ The phenethylamine family includes stimulants such as amphetamine and the human neurotransmitter dopamine, and mescaline shares some of their physiological properties: elevating mood, increasing the heart rate and banishing sleep. Its pronounced psychedelic qualities are absent or muted in other naturally occurring phenethlyamines, but have in recent years been created in synthetic mescaline relatives such as 2C-B, DOM and 2C-T-7.

There is much more to be learned about mescaline’s biosynthesis in cacti and its neurochemical activity in the brain, but none of it will solve the riddle of why a handful of cactus species should contain a potent psychedelic drug found nowhere else in nature. Mescaline is one of the few chemicals produced by plants in a dose concentrated enough to alter profoundly the way we think, feel and perceive the world around us. For the cactus, though, these properties may have no particular significance. Alkaloids, it seems, have no single and simple function in plants; they have probably evolved many times and for many different reasons. Recent research suggests that, in addition to their poorly understood metabolic roles, they may have coevolved with insects and animals: acting as poisons or deliriants for some and attractors for others, and thereby shaping the plants’ habitat in their favour.8 Within their microscopic ecologies of fungi and bacteria, any plants that develop a distinctive chemical profile are likely to have some advantage over their neighbours. Mescaline may be a step in a coevolutionary dance with other inhabitants of the desert, one that began long before the arrival of our species.

Human relations with the mescaline-containing cacti are ancient, complex, intimate and reciprocal. The much disputed taxonomy of the San Pedro family reflects the ease with which all cacti tend to hybridise, but it has probably also been shaped by localised human selection over millennia for short spines or high mescaline content. The deep valleys that rake across the Andes are ecological islands that breed their own distinctive varieties, with every imaginable combination of spine length, height, girth and skin colour. Trichocereus pachanoi, the classic San Pedro, typically has short spines growing in tight, regularly spaced clusters; the closely related Trichocereus peruvianus, which contains mescaline at similar or slightly lower concentrations, has spines that can be several inches long and needle sharp. Some cactologists treat T. peruvianus and T. pachanoi as long- and short-spined versions of the same species, while others regard them as only two species among a much more extensive family. Since the 1930s cactologists have used T. pachanoi as a rooting and grafting stock on account of its small spines, rapid growth and tolerance to a broad range of conditions, and there are now countless cultivar varieties worldwide.

Indigenous classification recognises many more varieties than western botany, defining them by their context and habitat as much as by a specimen’s individual characteristics. It also recognises different markers: for example, the number of ribs or columnar sections, ranging from four to eight, which meet at the tip and form a star shape when the cactus is cut into slices. Seven-ribbed specimens are highly favoured for magic and medicine but the four-pointed cactus, a rare variant analogous to a four-leaf clover, is regarded as the most potent. This is the form that appears to be carved in relief at Chavín.9

At 3,200 metres, Chavín stands at the upper limits of the San Pedro belt, beyond which the valleys rise above the treeline into the mist-shrouded grassland known as the puna. The cactus is a distinctive presence in the landscape: tall clusters are dotted outside the ancient site’s walls and cultivated around the local houses as fences and windbreaks. San Pedro’s precise role in Chavín’s ancient culture is, however, not so readily identifiable. The distinctive flora of South America includes many psychoactive species whose use dates back into deep prehistory. Sites from the Chavín period are decorated with representations of Brugmansia, the angel’s trumpet flower, whose leaves and seeds are a source of the powerful toxic deliriant scopolamine and its related alkaloids. Dried quids of coca leaves, found on the northern coasts of Peru together with the burnt lime with which to chew them, have been dated as far back as 6000 BCE. Tobacco’s centre of origin may well have been the Peruvian Andes, and its earliest cultivation is estimated at 5000–3000 BCE. By the time of the Early Horizon culture, maize and manioc were being fermented into chicha, a beer-strength alcoholic brew to which other psychoactive plants could be added.

Uniquely, the flora of South America also includes a variety of plants containing high concentrations of DMT (dimethyltryptamine). Though widespread in nature, including in trace amounts in the human brain, DMT is rarely present at levels potent enough for human use without chemical extraction. It is inactive when eaten or drunk, since enzymes in the human stomach break it down rapidly, but when snuffed at sufficient dosage it produces a burning sensation, an intense bout of nausea and brief, dazzling hallucinations. In the Amazon a concentrated dose can be sweated out over hot coals from the resinous bark of the virola, a jungle tree of the nutmeg family, or squeezed from the soaked roots of the spiny jurema (Mimosa hostilis). The DMT-rich leaves of chacruna (Psychotria viridis), a shrub related to the coffee plant, have long been boiled together with the yagé vine Banisteriopsis caapi, whose beta-carboline alkaloids make DMT psychoactive when consumed orally, into the emetic and hallucinogenic ayahuasca brew. In the Andes not far from Chavín, DMT is present, along with other related tryptamines, in the papery, disc-shaped seeds of Anadenanthera colubrina, a leguminous tree known in Quechua as vilca.10 Its close relative Anadenanthera peregrina, native to the Amazon, was brought to the Caribbean in around 500 BCE by the Taíno people; the first Spanish adventurers encountered it there under the name of cohoba.

The San Pedro cactus is the only psychoactive plant depicted in naturalistic style at Chavín,¹¹ but the presence of vilca is clearly attested by snuffing trays and tubes, artefacts that were widespread across the Andes in pre-Columbian times and are still in use by a few isolated groups today.¹² Vilca seeds, ground to a fine powder, were traditionally laid out on bone or wooden trays and snuffed forcefully with tubes, often made from the hollow bones of birds and sometimes combined into a Y-shape to propel the powder up both nostrils. Across Chavín-era sites from northern Peru down to northwest Argentina, these snuff trays and tubes have been found at many sites from 1200 BCE onwards. Trays made from whalebone have been unearthed hundreds of miles from the coast, alongside tubes fashioned from the bones of foxes and pumas as well as birds. It may be that vilca and San Pedro were also added to ceremonial chicha brews at this time, a practice witnessed in 1571 by Juan Polo de Ondegardo, a Spanish administrator in Cuzco.13

The consensus among its recent archaeologists is that Chavín was a temple built for large-scale ceremonies, and that hallucinogenic plant preparations were an important component of the rituals that took place there.¹⁴ The architecture of the complex seems to have been designed to frame and create a spectacle in which the senses were manipulated by sound, light and spatial disorientation as well as consciousness-altering plant preparations. Rushing mountain streams were rerouted to create an artificial watercourse that echoed through the tunnels; conch trumpet shells have been found, and fragments of anthracite mirror that may have bounced light through the galleries along with sound. The expansion of the site over centuries, and the replication of Chavín’s motifs in later sites hundreds of miles distant, suggest that the experience drew participants from great distances, uniting the cultures of the coast with those of the jungle on the Andes’ eastern slopes into which the Mosna river descends. For Julio Tello this made Chavín the founding nexus of Peruvian culture. He described it as the trunk of a mighty tree out of whose three great limbs – the coast, the mountains and the jungle – the nation had been born.¹⁵

Chavín places mescaline at the origins of South America’s first monumental culture, but in the company of too many other visionary plants to trace its signature clearly. The imagery that swarms across the temple’s stone reliefs is, to modern eyes, intensely psychedelic: a chaos of claws, jaws, wings and huge dilated eyes that resolves into geometrical, tessellated abstracts and stacked vertical repetitions. But this style suggests not so much the characteristic visions of mescaline as the fractal, bejewelled mindscapes that feature so prominently in contemporary DMT- and ayahuasca-inspired art. Chavín’s pantheon of fanged and bug-eyed deities are carved across vilca snuff trays and tubes from other, later cultural sites in Bolivia, Argentina and Chile. The consumption of DMT-containing snuffs is vividly suggested by the tenon heads on the walls that pour gouts of mucus from their noses as they grimace in ecstatic agony and shapeshift into feline predators, an ordeal still practised with similar snuffs by Amazonian shamans today.

The role played by mind-altering substances in the rites of long-vanished cultures can only be a matter for speculation, but the architecture of Chavín may offer some clues to how San Pedro was used. The pyramids, countersunk plazas and subterranean galleries constitute a vertical complex that appears designed for a sequence of ritual elements: a mass gathering, an ascent to the summit and a private ordeal or mystery, perhaps involving DMT snuffs, enacted in the labyrinths beneath. The imposing gate in the outer wall suggests a formal procession route into the temple’s ceremonial core. The gatherings in the plazas might have taken the form of singing and dancing enhanced by a San Pedro brew, perhaps as an admixture to a ceremonial chicha. Mescaline, like its modern stepchild MDMA (ecstasy), encourages rhythmic and stereotypic movement: in Mexican traditions, peyote was commonly used to drive celebrants through all-night dancing ceremonies. As well as moderating the nausea and uncomfortable physical symptoms of the cactus, rhythmic group movement on mescaline helps to bond celebrants together in a euphoric trance state. San Pedro could have performed this role for those who made the pilgrimage to the high mountains, as an element in a ceremonial brew that subsumed the inhabitants of desert, mountain and jungle into an ecstatic group mind and a shared Andean culture.

To judge by the archaeological evidence, San Pedro remained a prominent feature of the pre-Hispanic cultures that succeeded Chavín. Ritual vessels with cactus motifs are found among the Wari and Tiwanaku cultures in the highlands of southern Peru and Bolivia, where it is used in traditional healing to this day.16 The later Cupinisque, Lambayeque, Chimú and Moche cultures of Peru’s northern coast also produced ceramics and pottery featuring the cactus’s distinctive winding columns, working with the natural symmetry of its form. Stirrup-cups in which the San Pedro intertwines with the jaguar have been found in burial sites together with snuffing tubes and trays. In textiles on the coast further south, the cactus is commonly partnered with the jaguar or the hummingbird, a symbol today of the shaman’s power to suck malignant darts out of the victims of sorcery.

After the Spanish conquest, archaeological evidence was supplemented by fragmentary written testimony. In 1653 the Spanish priest Bernabé Cobo, who spent most of his life in Peru as a Jesuit missionary, witnessed the use of San Pedro and wrote of it in similar terms to those used by the Inquisition in Mexico to describe peyote: ‘this is the plant with which the Devil deceived the Indians of Peru in their paganism . . . transported by this drink, the Indians dreamed a thousand absurdities and believed them as if they were true’. (Cobo also recorded the use of vilca as an additive to chicha maize beer, and was one of the first Europeans to describe cinchona bark, the source of quinine. He suggested that San Pedro might share some of cinchona’s medicinal properties: ‘one can use its juice against fevers’.¹⁷)

It was only in the 1960s, with the identification of mescaline in the cactus and a new anthropological interest in syncretic urban cultures, that Peruvian ethnographers, pharmacologists and social psychiatrists began to investigate the secretive traditions of curanderismo or folk healing that had previously been dismissed as superstition, or at best as corrupted forms of the ‘pure’ shamanisms found in pristine cultures. Today, San Pedro curanderos are a distinctive presence in Peru’s northern coastal cities such as Casma and Trujillo. Large sections of the city markets are devoted to their trade – stalls crammed with wands, tablecloths and bottles of pungent floral scent, with thick stems of San Pedro stacked behind the counter – and practitioners’ painted signs, directing clients up narrow stairs to tenement rooms or back yards, jostle with those of astrologers, chiropractors and bus-ticket agents. In recent years a new genre of signs has emerged alongside them, lettered in English and illustrated with psychedelic designs of cactus stems and magical talismans, offering healing ceremonies in beach huts to western seekers. San Pedro shamans and healers are increasingly visible, too, in the jungle retreats of the booming ayahuasca tourist scene around Amazon towns such as Iquitos and Pucallpa.

San Pedro curanderismo as practised today incorporates many elements which are presumably of ancient provenance, but the ritual is shaped for modern sensibilities. It takes the form of a consultation between healer and patient in which a decoction of the cactus is drunk, sometimes by both participants but often only by the healer, as a catalyst to seek guidance from spirits or confront the powers of witchcraft. Prior to the ceremony, San Pedro stems are sliced into discs and boiled together with herbs for several hours in a metal pot. Unlike peyote, which contains a high enough concentration of mescaline to eat fresh or dried, San Pedro requires preparation to achieve a psychoactive dose.18 The resulting liquid is bitter to the taste and viscous in texture, and the dose is typically no more than mildly psychedelic in its effects: a languid, dreamy state, accompanied by mild nausea, and an expansive turn of mind that casts a clairvoyant glow over the proceedings. The brew is often given a herbal admixture to provide ‘heat’: sharpness and focus, to stop the subject from becoming too ‘cold’ and withdrawn. Many curanderos stir in a leaf or two of floripondio (plants from the Datura or Brugmansia genus), which adds a substrate of feverish energy along with a horribly parched mouth.

The focus of the ceremony is a mesa or table on which are arranged objects of special significance and power to the curandero: family heirlooms, ancient artefacts, animal remains, wands, bottles, feathers, effigies of saints. The space is cleansed with prayers and invocations to curandero ancestors and Christian saints, and tobacco smoke blown in the four cardinal directions; a liquid tobacco snuff is often taken by both participants to clear the head and please the spirits. As the effects of the mescaline build, certain objects on the mesa ‘catch the light’, announcing their particular significance and calling for interpretation. Curanderos spray perfume – usually a strong artificial rose or gardenia – to sweeten the air and honour the spirits; the inner gleam from the San Pedro infusion heightens the sparkle of the objects and the heady transport of the smokes and scents. The magically charged moment allows the curandero, with the assistance of the talismans, to project their awareness beyond the human range, opening up a sixth sense that reveals the hidden causes of things. A rattle or music may be used to conduct the spirits or reach out to a relative living far away; the configuration of the objects on the mesa may reveal the location of a lost possession. In cases of serious illness or psychic assault, the curandero may grab a wand from the mesa, leap up and do battle directly with the invisible source of the evil. By the end of the ceremony, when the psychic space is closed with prayer, the patient has been ‘opened up like a flower’, and the cause of their troubles plucked from them.19

Several years ago I joined a San Pedro survey expedition, collecting specimens from the valleys of Peru’s northern cordillera. We visited Chavín and Caral and the northern coastal town of Trujillo, where we bought cultivated stems of San Pedro, plump and glossy, from a herbalist in the market. Back in Lima on a rooftop terrace in the old Spanish district of Barranco, crowded with potted cactus specimens labelled by date, location and altitude, we sliced the stems and boiled them on the stove.

The internet teems with recipes for preparing San Pedro in more concentrated forms than the simple curandero method of chopping and boiling. Most of them are complicated, with several stages – freezing, skinning, boiling, reducing, fermenting – and their relative merits are vigorously disputed. We had no time for anything but the simplest: boiling chunks of cactus with the addition of cane sugar and lime to aid absorption and offset the bitterness. After a couple of hours the decoction was dark yellow, intensely bitter (a promising indicator of mescaline and its fellow alkaloids) and thick with ropes of mucus suspended in the liquid like raw egg white. Dosage was simply a question of how much we could hold down, in my case somewhere around half a litre.

We lay down on mats as the sun disappeared behind the roofs and over the ocean, and within minutes felt a sense of internal acceleration, gravity pressing us into the tile floor. Mescaline is notoriously slow to take effect, and it can often be two hours before the full measure of a dose is felt. Previously this type of simple brew had left me with little more than nausea, some physical heaviness and mild mental stimulation. This time, for whatever reason, I was immersed within twenty minutes in the paradoxical physical sensations of a strong mescaline dose. Languorous muscle relaxation combined with tremors, restlessness and nausea; fizzing euphoria with the ominous sensation of a fast-rising fever; a thrumming vibration in the chest with a cold heaviness in the limbs. As pleasure and discomfort mingled and intensified, it was easy to understand how some subjects feel themselves transported to the realms of the divine while others retire miserably to their sickbeds for the duration (a long wait). It was easy, too, to see why so many techniques had evolved to manage and work through these physical symptoms, whether by adding a stimulant to the brew or music and shuffling dance to the ritual.

As darkness fell, honeycombs of green and violet threaded across my vision. The cactus still sat queasily in my stomach but my blood pressure and circulation were recovering and the numbness and lassitude receding. In contrast to alcohol, as the peyotists of the Native American Church observe, with the cactus you get the hangover first. Standing up and stretching released warm rushes of energy, unlocking cramped muscles and pinched nerves. I thought of the thousands of cacti we had seen stretching and sprawling across the slopes of the mountain valleys as they luxuriated in the sun, each one a mescaline factory.

I walked over to the wall of the roof terrace, chest-high and surmounted with pots of cactus cuttings. It was Saturday night, and Barranco was coming to life. Below us was the dome of the ruined Spanish church of La Ermita, its beams visible through the collapsed plaster, and below it the ravine – el barranco – that leads through the cliff to a promontory over the ocean, a famous sunset spot from where crowds were slowly drifting back to the bars of the old plaza. In the centre of the view was the Puente de los Suspiros, spanning the ravine and connected to upper and lower walkways by stairs with black wrought-iron railings and balustrades. The panorama was mesmerising, and as I watched it took on the granular, hypnotic quality of a mescaline vision. The crowd seemed composed entirely of young couples, gazing off the bridge or strolling arm in arm; the bridges and railings became an Escher puzzle in which all were simultaneously ascending and descending. The streetlights against the tropical night made the scene into a rich chiaroscuro, balanced on the cusp between figurative and abstract. Like so many mescaline experimenters before me I reached for aesthetic references, and the sight obligingly moulded itself to fit them: Balinese shadow theatre, the silhouette animations of Lotte Reiniger, the technicolour abstracts by Oskar Fischinger that open Walt Disney’s Fantasia.20 Distant bubbles of laughter, chatter and accordion music resolved themselves into an orchestral soundtrack, then into tinnitus and back again.

Until this vision absorbed me, I had been entirely immersed in the strange alterations in my sensorium. Now I was nowhere in the scene, no more conscious of myself than when caught up in a movie. The scene in front of me might have been endless, or it might have been a short repeating loop; I had, in another familiar refrain of mescaline’s subjects, stepped outside of time. At some point in the small hours the crowds filing across the bridge must have thinned, but my next distinct memory is of the sky brightening, the early morning jet trails slicing pink webs across it, as the spell of the San Pedro slowly faded.