The highest peak in the region and the most prominent land formation, the Üçhisar Castle is a larger-than-life sculpture. A climb up the 120 steps to the summit of the fortress is a logical introduction to the rocky scapes of Cappadocia. In the 15th and 16th centuries, the Byzantine army took advantage of the natural elevation of three of the area's rock formations and used them as natural fortresses. Üçhisar, together with Ortahisar and a rock castle at Ürgüp (now in ruins), provided the means for an early warning system using mirrors and lights, sending messages among the fortresses and as far afield as Istanbul. Today the outer layers of Üçhisar's rock have been washed away by erosion to reveal a honeycombed structure of tunnels and cavities, rising above the man-made facades of the modern semi-troglodyte village. Recently discovered was a secret tunnel leading to the riverbed, which provided an emergency water supply in the event of an attack.