Torre medieval de Martiartu, located in Erandio, Bizkaia, is a defensive and residential tower constructed in the 14th-15th century by Martín Ortiz de Martiartu, though its current 16th-century exterior appearance masks its medieval origins. Built with sandstone masonry of decreasing wall thickness with height, the tower once strategically dominated the Udondo valley and controlled trade routes between Plentzia and Bilbao. The fortification combines military and residential characteristics and remained inhabited until its abandonment. Destroyed in 1472 by Ochoa Ortíz de Gueches, it was rebuilt in the early 16th century by Diego Pérez de Martiartu, preserving elements of the original structure and representing an important example of Basque medieval architecture.
