La Grande Tranchée | canal de Nantes à Brest

Known as "la Grande Tranchée", because of its length and construction, or "la tranchée des bagnards", in reference to the convicts and prisoners who worked to clear this valley, this work gained notoriety thanks to Jean Kergrist, who recounted the adventures of the camp workers in a book entitled "les bagnards du canal de Nantes à Brest".

The trench, dug in the 19th century, was over 3 kilometers long, 100 meters wide and 23 meters deep, and took 9 years to complete.

The 4,000 Glomel convicts had to move as much earth and rock as it would take to build a great Egyptian pyramid. Three million cubic meters of earth were removed with shovels and pickaxes and transported by cart or on men's backs. The living conditions and hygiene were unimaginable, and the work so hard that many of the convicts succumbed to illness and death.

The impressive trench, the highest point of the canal at 184 meters above sea level, allows the Aulne and Blavet watersheds to communicate via the canal.

The site is classified as a Natura 2000 protected area, due to its fauna and flora. It adjoins the Lan Bern moors Regional Nature Reserve.