Les Cammazes and the Vauban vault, at the source of the Canal du Midi

High in the Montagne Noire, Les Cammazes hides a tunnel by Vauban that carries the water of the Canal du Midi. Vault, channel, lake and forest: our guide to a perfect day out.

Les Cammazes is a small village in the Tarn, perched on the Montagne Noire (the "Black Mountain") about half an hour's drive from the Château du Falga, via Revel and Saint-Ferréol, in the Lauragais near Toulouse in south-west France. People come here for the voûte Vauban, the Vauban vault: a tunnel of about 120 metres, dug in the late 1680s, through which the water of the rigole de la Montagne (the mountain feeder channel) passes beneath the village to reach the Laudot stream and then the lake of Saint-Ferréol, the great reservoir of the Canal du Midi. Around it lie a tree-lined channel with a perfectly flat path, a large dam lake, the forêt de l'Aiguille and a quiet village more than 600 metres above sea level. It is one of our favourite outings when summer grows too hot in the plain.

Why a tunnel under a mountain village?

To understand the vault, we have to go back to the problem that occupied Pierre-Paul Riquet all his life: how to supply water to the highest point of the Canal du Midi, the seuil de Naurouze, which boats cross between the Atlantic and the Mediterranean. The answer came from the Montagne Noire, where far more rain falls than in the Lauragais. Riquet had a channel dug there to gather the mountain streams and lead them, valley by valley, down towards the plain. Work began in 1667, the year the first stone of the Saint-Ferréol dam was laid.

In Riquet's design, the rigole de la Montagne ended at Le Conquet, a neighbouring hamlet, where it flowed into the Sor river; the water then ran down to the plain and into the rigole de la Plaine. The Saint-Ferréol reservoir, meanwhile, was fed only by the modest Laudot stream. Riquet died in 1680, a few months before the canal was filled with water in 1681. What remained was to make sure the waterway would never run dry.

What does Les Cammazes owe to Vauban?

In December 1685, Vauban was given the task of inspecting the canal. The commissioner general of fortifications travelled along it in early 1686 and found silting and sand build-up. He proposed a whole programme: canal bridges so that the canal no longer crossed rivers at their own level, new locks, and the raising of the Saint-Ferréol dam. And, up on the Montagne Noire, an extension of the channel beyond Le Conquet, to tip part of its water into the Laudot valley and fill the reservoir further.

Between the two valleys rises a rocky ridge, exactly where the village of Les Cammazes stands. Rather than going around it, the engineers went through it. The plans were Vauban's; the works were led by Antoine Niquet, director of fortifications for Languedoc, who went on to manage the canal until his death in 1726. The cutting was dug in 1687 and 1688. The work was dangerous: an accident in April 1687 killed six workers and injured three.

The result is a masonry tunnel about 120 metres long (sources give between 121 and 123 metres) and about 3 metres wide, known ever since as the voûte Vauban. In the 19th century, trees were planted above the cutting (1846) and a house was built for the vault's keeper (1847). Together with the canal, the feeder channels and the reservoirs, the structure is part of the site inscribed on the UNESCO World Heritage List in 1996.

What is it like to walk through the vault?

You enter the vault on foot, and only on foot. The way through is a narrow ledge running along the wall, above water slipping by in the half-light. There is neither lighting nor handrail: bring a head torch or, failing that, your phone's flashlight, and good shoes. Halfway along, all you can see are two small patches of daylight, one behind you, one ahead. It is a striking, very physical moment, when you grasp what such a project meant, built with picks and gunpowder.

A few tips from our own outings:

• park in the car park near the vault, where there is also a picnic area;
• take a proper torch and keep your hands free to steady yourself against the wall;
• bicycles cannot go through the tunnel, and animals are not allowed;
• hold young children by the hand: the ledge is narrow and the water very close;
• in summer, the coolness of the vault is a real joy after the heat of the Lauragais.

Which walk to take along the rigole de la Montagne?

As you leave the tunnel, an almost flat path follows the channel beneath tall trees. It is the ideal family walk: no climbing, water at every step, shade in every season. The path leads to the saut du Laudot, a masonry waterfall of about 8 metres through which the channel's water joins the stream that runs down to Saint-Ferréol. You can also follow the channel the other way, towards Le Conquet and the valleys where it gathers its water.

For walkers, several waymarked loops start from the village, on foot, by bike or on horseback; among them is a circuit of about 7.5 kilometres dedicated to Vauban. The tourist office website Aux sources du canal du Midi details the routes and practical information. The most energetic can follow the channel much further: it runs for more than twenty kilometres from the Alzeau intake, above Arfons, passing near the lac du Lampy, a reservoir added between 1777 and 1782.

What should you know about the lac des Cammazes?

Just below the village, the lac des Cammazes belongs to quite another age. The dam, a concrete arch about 70 metres high, was built on the Sor from 1954 to 1957 and brought into service in 1958. The reservoir covers nearly 90 hectares and holds about 18.8 million cubic metres. It is managed by the Institution des eaux de la Montagne Noire and serves first and foremost for drinking water: more than 170,000 people in some two hundred municipalities drink water from the Montagne Noire. It is also used for irrigation and acts as a reserve for the Canal du Midi.

The two systems, Riquet's and the 20th-century one, are connected: the lake receives surplus water from the channel through the Conquet overflow, and conversely an intake can top up the channel. Here, three centuries of hydraulic engineering are layered over just a few kilometres. As the lake is a drinking-water reserve, swimming is not the main attraction: people come above all for the views from the road and the paths around it. For a swim, the nearby lake of Saint-Ferréol is the place to go.

Which forest surrounds Les Cammazes?

The village is wrapped in the forêt de l'Aiguille, a former royal forest that is now state-owned, part of which is protected as a biological reserve. This is the Montagne Noire as we love it: tall trees, damp undergrowth, paths where you meet more roe deer than walkers. Around a bend you come across the last restored charcoal "marmites", great steel cauldrons in which charcoal was made in the 20th century, an activity that stopped in 1958. They tell of another side of the mountain, that of the charcoal burners and foresters.

The climate here is unusual: the Montagne Noire is under both Atlantic and Mediterranean influences. It is often a few degrees cooler than in the plain, which makes it a precious refuge during heatwaves.

What is the village of Les Cammazes like?

Les Cammazes has about 400 inhabitants, on a plateau between the valleys of the Sor and the Laudot, at the gateway to the Parc naturel régional du Haut-Languedoc. The village grew up around the old castrum of Roquefort and expanded in the 17th century with the building works on the channel and the lake of Saint-Ferréol: its history is closely bound up with that of the canal. There is a park above the vault, perfect for a picnic, a fountain, and a few places for a break, including a tearoom named after Vauban.

The day falls easily into place. In the morning, the vault and the channel down to the saut du Laudot; a picnic in the park; in the afternoon, the forest or a walk around the lake, then down to Saint-Ferréol for a swim and a stroll along the dam. Returning via Revel, you will have followed the whole chain of water, from the mountain down to the plain of the Lauragais.

How does Les Cammazes fit into the rest of the canal system?

Les Cammazes is just one link in a remarkable network that you can discover over several outings from Le Falga. The lake of Saint-Ferréol, completed in Riquet's day, stores winter water for the summer; its dam was raised in Vauban's time and has been protected as a historic monument since 1997. Further down, the rigole de la Plaine carries the water to the seuil de Naurouze, where it divides between the two seas. The official Canal du Midi website gives a clear account of this Montagne Noire water supply, from the Alzeau intake to the watershed. We have also devoted two articles to it: the lake of Saint-Ferréol and the Montagne Noire feeder channel.

Frequently asked questions

How long is the Vauban vault?
About 120 metres; depending on the source, between 121 and 123 metres, and about 3 metres wide. It takes a few minutes to walk through.

When was the Vauban vault built?
It was decided after Vauban's inspection in 1686 and dug in 1687-1688 under the direction of Antoine Niquet, to Vauban's plans.

Can you walk through the vault with children?
Yes, holding young children by the hand and with a good torch: the way through is a narrow ledge, with no lighting or handrail. Bicycles and animals are not allowed in the tunnel.

Can you swim in the lac des Cammazes?
The lake is primarily a drinking-water reserve; for swimming, we recommend the nearby lake of Saint-Ferréol.

Staying at the Château du Falga to explore the Montagne Noire

From Le Falga, the Montagne Noire is our summer garden: we drive up in the morning, come down for a swim at Saint-Ferréol, and return for dinner on the south-facing terrace. The château welcomes up to 21 guests around its pool and park; the Petite Maison, rented separately, sleeps 4 all year round. To plan your stay or ask for our favourite routes, write to us. And to round off the day, discover Revel and its market or the abbey school of Sorèze.

Sources: Canal du Midi (official website, Montagne Noire water supply and lake of Saint-Ferréol); Tarn Tourisme; Aux sources du canal du Midi tourist office; Les Cammazes brochure (Haute-Garonne Tourisme); Réseau Vauban (Cammazes fact sheet); Wikipedia (Les Cammazes, Barrage des Cammazes, Rigole de la Montagne).