Madrid was founded on a Qanat system, the sophisticated water engineering developed during the North African Golden Age of Engineering that move Acequia practice across the arid coast of the southern Mediterranean through Morocco and into the Iberian Peninsula as al-Andalus was being established in the 9th century. Qanats tap into a hillside aquifer & pull a vein of water to the surface at a higher altitude than the natural spring, to supply a settlement with water, which in turn supplies downhill acequias with water for crop fields.

These street rubbings were made outside a surviving Qanat in Madrid during an excursion while on a residency with AADK looking at acequias in the Huerta (or Garden) region of South Central Spain.