Strabo Geography 4.6.5

[5] After the Vocontii, are the Iconii, the Tricorii, and the Medulli; who inhabit the loftiest ridges of the mountains, for they say that some of them have an almost perpendicular ascent of 100 stadia, and a similar descent to the frontiers of Italy. In these high-lands there is a great lake; there are also two springs not far distant from each other; one of these gives rise to the Durance, which flows like a torrent into the Rhone, and to the Durias, ¹ which flows in an opposite direction; for it mingles with the Po after having pursued its course through the country of the Salassi ² into Cisalpine Keltica. From the other source, but much lower down, rises the Po itself, large and rapid, which as it advances becomes still vaster, and at the same time more gentle. As it reaches the plains it increases in breadth, being augmented by numerous [other rivers], and thus it becomes less impetuous in its course, and its current is weakened. Having become the largest river in Europe, with the exception of the Danube, ³ it discharges itself into the Adriatic Sea. The Medulli are situated considerably above the confluence of the Isère and the Rhone.