Strabo Geography 4.6.7

[7] A great part of the country of the Salassi lies in a deep valley, formed by a chain of mountains which encloses the district on either side; a part of them however inhabit the ¹ overhanging ridges. The route of those who are desirous of passing from Italy over these mountains, lies through the aforesaid valley. Beyond this the road separates into two. The one which passes through the mountain peaks, known as the Pennine Alps, cannot be traversed by carriages; the other, which runs through the country of the Centrones, lies more to the west. ² The country of the Salassi contains gold mines, of which formerly, in the days of their power, they were masters, as well as of the passes. The river Doria Baltea ³ afforded them great facility in obtaining the metal by [supplying them with water] for washing the gold, and they have emptied the main bed by the numerous trenches cut for drawing the water to different places. This operation, though advantageous in gold hunting, was injurious to the agriculturists below, as it deprived them of the irrigation of a river, which, by the height of its position, was capable of watering their plains. This gave rise to frequent wars between the two nations; when the Romans gained the dominion, the Salassi lost both their gold works and their country, but as they still possessed the mountains, they continued to sell water to the public contractors of the gold mines; with whom there were continual disputes on account of the avarice of the contractors, and thus the Roman generals sent into the country were ever able to find a pretext for commencing war. And, until very recently, the Salassi at one time waging war against the Romans, and at another making peace, took occasion to inflict numerous damages upon those who crossed over their mountains, by their system of plundering; and even exacted from Decimus Brutus, on his flight from Mutina, ⁴ a drachm per man. Messala, likewise, having taken up his winter quarters in their vicinity, was obliged to pay them, both for his fire-wood, and for the elm-wood for making javelins for the exercise of his troops. In one instance they plundered the treasures of Caesar, ⁵ and rolled down huge masses of rock upon the soldiers under pretence of making roads, or building bridges over the rivers. Afterwards Augustus completely overthrew them, and carried them to Eporedia, ⁶ a Roman colony which had been planted as a bulwark against the Salassi, although the inhabitants were able to do but little against them until the nation was destroyed; their numbers amounted to 36,000 persons, besides 8000 men capable of bearing arms. Terentius Varro, the general who defeated them, sold them all by public auction, as enemies taken in war. Three thousand Romans sent out by Augustus founded the city of Augusta, ⁷ on the spot where Varro had encamped, and now the whole surrounding country, even to the summits of the mountains, is at peace.