San Juan y Sanz y Fores and Plaza de Juan XXIII are both on the route from Plaza Porlier to Calle del guila. Prior to 1887, it was known as “Calleja de San Juan,” but in honor of the German mining engineer Guillermo Schulz y Schweizer (1805–1877), whose works include the Geological Map of Madrid and Generals of the Kingdom, it now has its current name. In El Libro de Oviedo (1887), Fermn Canella y Secades gives the following description of it.
Before, Calleja de San Juan, Schultz. The original structure, or altar, of the former Parish Church of San Juan was given to the cathedral by Alfonso the Great. Pope Alfonso VI established the temple, which served the hospital directly. It was destroyed in 1869 and replaced with a splendid Byzantine portico from the early 12th century, embellished with molded coffered ceilings that were graceful and diverse. The tapered vault is flanked by the capital, three pillars, and carved corbels. , close to La Puerta, resembles a 14th-century tomb. The contemporaries of that portal were shafts with capitals attached to the buttresses of the main arch, though the entire church was later remodeled, including the apse, the interior chapel, the chapel dedicated to the Mass Brotherhood, and the pointed brick arch. There are numerous claims that the remains of King Silo and his wife Adosinda have been removed, but there is a pantheon of the Ordonez family on land; nevertheless, neither the altar built by Bishop D. Pelayo nor the tomb, where there are no foundations, have any safe remnants. The church, which had been deemed a ruin, was destroyed in 1882. The artistic cover fragments were catalogued, collected by the Provincial Board of Monuments, and placed in a municipal deposit for the bishop’s use. The enclosure was also expanded, and a portion of the adjacent hospital was destroyed. This left a wide street with the name of the sage mining engineer D. Guillermo Schulz, an adopted Asturian, in honor of the well-known topographic map. -Int. : San Juan; -Conc. : Lorenzana.