 In Roman times, it was known as the "Vatrenus" (small "Renus"), although, in the Tabula Peutingeriana, it was already identified as the "Santernus".It rises near the Futa Pass, at of elevation, in the Apennine ridges facing the plateau of Firenzuola in the province of Florence.Beyond Firenzuola, it flows northeast through the province of Bologna near Castel del Rio, where it is crossed by a famous medieval bridge, the "Ponte degli Alidosi".