Work on this cathedral, which stands on the site of the original building, began in the 12th century, in 1124 to be precise, at the command of the first bishop after the Christian Reconquest, Don Bernardo of Agen. Construction continued throughout the Lower Middle Ages, and the cathedral was finally completed in the 15th century, after which work began on other dependencies (sacristy, ambulatory, etc.), as well as all the ornamentation, altars, etc.

The portals (south and west) are Romanesque, pertaining to the original cathedral, though with later neoclassical and Baroque additions. On either side of the portal are robust towers built in the medieval military architectural style.

The cathedral originally stood within the city walls, which were demolished to accommodate extension work on the cathedral itself and in the Plaza Mayor or Plaza del Mercado, built to the south in the 16th century. Other dependencies, the cloister and other courtyards, surround the cathedral, making it independent from the rest of the city.

The cathedral’s presence gives tone and atmosphere to the city of Sigüenza, which is articulated around it both historically (it was the feud of the bishops for eight centuries) and architecturally.

The cathedral exterior is a model of church-fortress architecture, an exceptional monument due to its size and distinction, outstanding due both to its religious category and its architectural importance.