The Transparente in the Basilica of the Monastery of El Escorial

The presbytery of the basilica of the Monastery of San Lorenzo de El Escorial is closed on its eastern side by a monumental altarpiece that, apparently, is attached to the thick outer perimeter wall. However, at the height of the lower section and behind it, there is a vaulted space that has not yet been studied, and whose main interest is its function as a Transparente. This architectural device, a precursor of other solutions used later during the Baroque period, allows the rays of the rising sun to be introduced directly into the tabernacle and onto the high altar through a window positioned for this purpose. Our study deals with the succession of vaulted and lintelled spaces, arches and windows that make it possible to achieve such a singular effect, together with other aspects related to the perception of the whole, and to the geometry of light.