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In Vallinfante di Castelsantangelo sul Nera, in the heart of the Sibillini Mountains National Park, a vein of spring water emerges from the thick layers of debris accumulated in the bottom of the Infante valley, giving rise to the Nera river. But once upon a time, according to legend, the waters of the river flowed from two cavities similar to the "nostrils" of an animal. In the initial stretch it is just a stream, yet the Nera is the main tributary of the Tiber so much so that, as the Romans well know, "the Tiber would not be the Tiber if it weren't for the Nera to give it to drink".