The River Tarn
Cité épiscopale d’Albi
The river Tarn, from the Latin ’Tarnis,’ which, according to the etymology of its Celtic name, means both ’rapid’ and ’steep sided,’ separated Gallia Narbonensis (Narbonese Gaul) from Gallia Aquitania (Aquitaine Gaul).
The source of the Tarn is in the shale of the Lozère hills at an altitude of 1550 metres (5000 feet). Throughout its course it has forged picturesque limestone gorges and receives the waters of many tributaries, the tarnon, the dourbie, the agout and the aveyron as it passes through the towns of Southern France, the best known being Albi and Montauban.
The river bed has dug its way down between steep banks. With one of its tributaries it defines a triangular plateau which tapers at its western end into a spur which culminates 30 metres above the waters.
Upstream of this promontory the banks of the Tarn become less abrupt to the point that it was once possible to cross the river here via a ford. The location of the ford is still marked by the mills that were built here. An excellent defensive site at the heart of fertile plains and close to a river crossing, and at the meeting point of diverse regions (the ’cold lands’ of the Ségala, the ’Causses’ (limestone plateaux) around Cordes-sur-ciel, and heavy, clay soiled hills), such are the natural advantages which led to the establishment of a settlement at Albi.
As it arrives at the border of the Department, the bed of the Tarn is a layer of marl, an excellent source of lime for constructions that are exposed continually to water such as dykes, mills and locks.
Almost everywhere, the river bed demonstrates a great variety of constituents: white, black, grey and red quartz, green and red porphyry, often combined with feldspar, volcanic lave, marble and granite of variable qualities.
The Tarn flows over a course of 375km and its basin, for the most part in the Massif Central, covers more than 12,000km². Its flow is variable, it averages 140m²/second but reached more than 8000m²/second during the historic flooding of 1930.
The waters of the Tarn take only 5 hours to traverse the Department. In addition to fish such as gudgeon, bullheads, and sucker fish, we find the occasional lamprey, rainbow trout, eel and catfish.