Built between 1562 and 1595, in berroqueña stone, it had a length of 36.9 km, height between 1 and 1.5 meters and width of about 50 centimeters. Its main purpose was to serve as a limit and demarcation of the properties acquired by Philip II to endow the monastery with its own resources (La Herrería, La Fresneda, La Granjilla, El Campillo and Monesterio). It also served as an element of defense against intruders; of protection of the pastures destined to the oxen used in the construction of the monastery; as dehesa and real forest of hunting; and as a sanitary belt for a smallpox infection.
Later Charles IV would raise the height of the wall, raising the jumps, so that the hunt could enter but not leave and solve, in this way, the problems that, since Philip II’s time, had been causing the animals of the hunting ground real in the crops and livestock of the local peasants.
It is accessible from Zarzalejo following the so-called circular small route of 8 km. and medium difficulty. On the way to the Quemadillo, we ascend to the Entre Cabezas pass, where we find a fountain that serves as refreshment for the senderista. After leaving this, a few meters higher, we will have reached our destination. From there, ascending towards the summit of the Machota Grande (1,464 meters), you reach the rock of the Fraile, a peculiar mass of berroqueñas stones that remember the figure of a praying monk.
The descent gives us spectacular views of the Sierra de Guadarrama, San Lorenzo de El Escorial, Mount Abantos, etc.