Tacked on to a sheer rock face, a series of weathered wooden channels led our hiking group across vertical cliffs at a dizzying 1,200m. It was only thanks to the mounted guardrails and safety nets that we could walk the 6km-long trail – known as Torrent Neuf – at all. The 15th- Century Rhône Valley farmers and vintners who dared to build these suspended irrigation channels had nothing more than a shovel, pickaxe and worn ropes. It was a perilous job that cost lives – but spared one corner of Switzerland from near drought.
Switzerland may be dubbed "Europe's water tower", but one region, the Valais in south-western Switzerland, has historically endured aridity exacerbated by the foehn, a notoriously dry, warm wind found here.
Bordering Italy to the south and France to the west, the L-shaped region stretches from the mighty Matterhorn to Lake Geneva. The alluvial soils of lower Valais' gentler slopes are carpeted with fruit orchards, where some 70 varieties of apricots ripen in the region's Mediterranean-like summers. Meanwhile, in the exposed alpine pastures of German-speaking upper Valais, native breeds like Valais Blacknose sheep and horn-locking Herens cattle clang their bells in the shadow of the Alps. These same 4,000-plus metre peaks protect central Valais' terraced vineyards that green the dramatic Rhône Valley's south-east facing slopes. This is the heart of Switzerland's boutique wine industry, where endemic varieties like Amigne and Goron de Bovernier have put Swiss vintages on the world map.
Despite being surrounded by some of Switzerland's wettest mountains, the sun-scorched, glacier-carved region receives just 500mm of rainfall a year, presenting a unique engineering challenge for irrigation. Cue gravity-defying bisses, designed to divert glacial meltwater from mountain streams to parched pastures and vineyards at lower elevations. To this day, 200 of them totalling 1,800km in length supply water to 80% of the Valais' irrigated land.
The Valais, which stretches from Lake Geneva to the Matterhorn, is the driest region in the country (Credit: sbossert/Getty Images)
Measuring between 0.5m to 2m in breadth, the most primitive of Valais bisses were hewn out of rock. Others, like the 500-year-old Bisse des Sarrasins in the district of Sierre in central Valais, were hollowed from tree trunks. But the true marvels of bisse engineering were the "hanging channels", designed to guide water from far-off glaciers around gorges and overhangs in the region's wildest corners.
Located 1,200m above the east bank of the Morge River in Savièse (a sub-region of Central Valais), Torrent Neuf's 15th-Century hanging channels were built specifically to capture glacial milk before it entered a gorge. Using larch felled from the nearby Foret du Ban du Torrent, workers crafted a series of three-sided wooden conduits that could buffer against avalanches and rock-fall. A real high-wire act, the men would hang at the ends of ropes, anchoring these hanging channels to the sheer limestone cliffs with a double row of wooden beams called boutzets.
After watering the thirsty plateau of Savièse for five centuries, Torrent Neuf's hanging channels were retired in 1935. Credited with heralding the golden age of bisses in the 1400s thanks to its success in irrigating unproductive land, Torrent Neuf Bisse was restored in 2013 as a piece of cultural heritage.
In the Valais' lower valleys, bisses were earthen cut. The excavation debris buttressed the channel's outer banks, like in Torrent Neuf's forested downstream segment, known as Bisse de Ste Marguerite. Fed by the Tsanfleuron Glacier, Saviésans like Lydwine Bruchez continue to draw water from it. The farmer grazes horses, Héren cattle and a flock of 120 organic Suffolk sheep on her 60 hectares.
"Thanks to the bisses we [farmers] have fodder for our animals. It is a question of survival for Valais agriculture," Bruchez told me. "Water is life, quite simply."
Known as the "King of Bisses", the Bisse d'Ayent is honoured on the nation's 100-franc note (Credit: Van der Meer Rene/Alamy)
On a stifling hot day in May, I watched in disbelief as a lithe Bruchez launched a 5kg iron plate (a family heirloom) into the air, before plunging it into a small channel of water running through her flower-freckled meadow. The action – based on an age-old practice known as "zetti" – diverts the water temporarily to flood farmers land by runoff. Minutes earlier, Bruchez had raised the sluice gate of a small bisse located scarcely 100m away to create the artificial water channel.
It is a question of survival for Valais agriculture. Water is life, quite simply.
Normally the sole key-bearers of these small hand-operated sluice gates are bisse guards like Philippe Emery, whose responsibilities include maintaining and cleaning the bisse and coordinating the distribution of its water. He's been caretaker of Savièse's Bisse de Lentine – located above the Valais medieval capital of Sion – for 13 years.
Bordered by a retaining dry-stone wall, the 4km-long Bisse de Lentine is skirted by a path overhanging stepped vineyards, stretching along the Rhône's northern bank. The sight of a scuttling scorpion is a clue to the Valais semi-arid climate, where six species of cactus thrive, alongside figs and snakes.
"I found a 2m-long viper lurking here once," Emery remarked, cautiously squatting over the bisse to remove the metal plate that raises the water level. Unpadlocking the sluice gate he then redirected the bisse water to a nearby 200-litre metal barrel. These private and community-owned "reservoirs" are where local vintners draw water for their vineyards, usually starting in May when the rain tails off, continuing into September.
No parcel of land is left unutilised by the region's indefatigable winemakers, who work some of the world's steepest vineyards. Owner of nearby Cave L'Orpailleur, Frédéric Dumoulin, tends to plots measuring just 1,000sq m. Clinging improbably to 30-degree gradient slopes, his Chardonnay vines grow at 900m.
The 5kg iron plate that Lydwine Bruchez uses to divert waterflow is a family heirloom (Credit: Sarah Freeman)
All 20 of Dumoulin's grapes (including indigenous varietals like Petite Arvine) are nourished by Clavau – a bisse built in 1453 by the Bishop of Sion. Thanks to its snow-capped Alpine views and direct access to guérites (wine bars), the Bisse de Clavau doubles as a well-trodden hiking trail. It's one of a raft of mercifully flat bisse walks in the region that have proven a boon for regional tourism.
Starting at the village of St-Romain, Bisse de Clavau's 8km-long path weaves through vertiginous vineyards that tumble down to the Rhone River – a ribbon of shimmering turquoise flanked by emerald-green slopes. I followed the sound of droning bees and babbling water that flowed alternately through the bisse's open-air concrete channels, stone tunnels and metal conduits.
One person who knows more about the region's ancient watercourses than most is bisse veteran Jean-Charles Bornet. Raised in the folds of Nendaz's sun-drenched valley – home to the Valais' largest network of bisses – the local councillor's happy place is Bisse Vieux. "I remember hiking up here as a boy with a huge picnic rucksack that weighed more than me," Bornet remarked as we followed the bisse's contours beneath towering spruce trees. "It's where I spent many a weekend, and still do.
First written about in 1640, 1,600m-high Bisse Vieux is unique in conveying water year-round, tapped from the Pennine Alps Grand Désert Glacier. It's also a textbook example of how this indigenous irrigation technology was adapted for challenging terrain. Midway along its 7km course, water cascades down a series of stepped metal troughs, which plunge 5m to navigate a rocky ridge. On a flatter stretch, Bornet gestured to the remains of a huge boulder resting on the bisse's bank, shattered by dynamite. "This was a job for a local apricot farmer who happens to have a dynamite license," he said, explaining that rocks unstuck by melting snow and natural debris like branches can often obstruct the bisse, requiring some "explosive" intervention.
Crossing several watersheds, longer bisses like the 26km one in the village of Saxon were an easy target for water thieves in the 1300s. The solution? A water-driven warning hammer lifted by a paddle wheel at every turn, which still works today. Guards would overnight in wooden cabins alongside them, ready to pounce if the hammer went mute, which could also signal a blockage in the bisse upstream.
The bisses divert glacial meltwater from mountain streams to pastures and vineyards at lower elevations (Credit: Sarah Freeman)
"Nowadays a guard can know just with the sound of the water if a stone is blocking it somewhere along its course," Bornet said, while dislodging a branch from the bisse.
While many Swiss outside of the Valais won't have heard of bisses, the 100-franc bill is adorned with an illustration of one of the most spectacular: Bisse d'Ayent. Built in 1442, its passage of hanging channels that cling to a 1,800m rocky ridge are a feat of engineering that have earned it the moniker "King of Bisses". "The bisses are the result of the ingenuity and audacity of the Valais and its people," head of European markets for Valais Tourism Board, Emilie Morard told me. "We are proud of this ancestral know-how."
Ancient Engineering Marvels is a BBC Travel series that takes inspiration from unique architectural ideas or ingenious constructions built by past civilisations and cultures across the planet.
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