Shaped by water and enclosed between the Prenestini, Ruffi, Simbruini and Lepini mountains, the Aniene Valley boasts a landscape of extraordinary complexity, where nature and history intertwine in a continuous process of transformation. Between Rome, Tivoli and Subiaco lies a territory that, along the seventy kilometres of the Via Tiburtina, showcases ancient and recent anthropic traces, capable of restoring the memory of a never-ending dialogue between man and the environment. This guide offers a new interpretation of the Valley through interdisciplinary scientific contributions that describe sacred spaces and highlight a living, fragile and precious landscape: a threshold between the Ager Tiburtinus and the mountains, to be rediscovered with a new and mindful gaze.