The walls of the castles and fortresses had to resist not only the mechanical actions but the attacks with projectiles and rams. For this reason, the walls had to be reinforced with wooden chains in their interior. This reinforcement also prevents the quick ruin in the case of the opening of a breach in the wall and facilitates the fast reconstruction. Depending of the building technique, the wooden reinforcing is different. In walls built with rammed earth or formworked masonry, the branches and beams are laid inside the earth or the lime and rubble. The walls built with stone masonry and ashlars or brick, the wooden beams functions reinforcing the internal filling. This polyorcetical and building technique has been referred by several ancient authors, as Vitruvius or Philo of Byzantium. They recommended the use of wooden beams inside the walls and their recommendations were learnt during Middle Age.
There are Spanish Medieval fortifications in where the wooden reinforcement is visible nowadays. The ruins of the castles show the building ‘section’ of the walls. Thus, the reinforcing system can be studied and traced. Usually, wood has rotted and only remains its negative in the mass of the wall. Notwithstanding this lose, in several cases, wood has been preserved or the design of the reinforcement can be drawn.