The Church of Saint John the Baptist is located where most likely a Roman temple dedicated to Bacchus used to be, and later became a Jewish synagogue. In fact, the church is located in the old Jewish quarter of the city.
The temple, of late Gothic style, began its construction in the first third of the 16th century. Since then it has undergone several renovations, being practically destroyed in 1936 as a result of the events of the Spanish Civil War. Its typical Plateresque façade stands out, its beautiful and stylized octagonal tower and the rich Sagrario, made by the Archpriest of Arjona Juan Antonio León.
The Church of San Juan Bautista is only mentioned once in the book, specifically on the last page, but it is of great importance, since it is where the Templar Tombstone was found, in an underground burial (the Crypt of Baron of Velasco, aka Barón de Velillos in the novel).
Likewise, the fact of being consecrated to Saint John the Baptist is another nod to the Templar Order, since one of the theories of some scholars indicates that the Baphomet Templars symbolized Saint John, whose head they would have found in excavations in the Holy Land and that the Templars would have embalmed, so these representations would refer to the Saint.