The last bishop-lord, known as the "mason-bishop", built a neighborhood below the level of the old town in a Neo-Classical style, before renouncing to the temporal lordship.
After the war, their city limits increases with the incorporation of 28 pedanías: Alboreca, Alcuneza, El Atance, Barbatona, La Barbolla, Bujalcayado, Bujarrabal, La Cabrera, Carabias, Cercadillo, Cubillas del Pinar, Guijosa, Horna, Imón, Matas, Mojares, Moratilla de Henares, Olmedillas, Querencia, Palazuelos, Pelegrina, Pozancos, Riba de Santiuste, Riosalido, Torrevaldealmendras, Ures, Valdealmendras, Villacorza.
The cathedral is a very massive Gothic edifice of ashlar stone, though the lower levels show it was built on the Romanesque cathedral. Its façade has three doors, with a railed court in front. At the sides rise two square towers, 164 feet high, built on different times, with merlons topped with large balls; these towers are connected by a balustrade which crowns the facade, the work of Bishop Herrera in the eighteenth century. The interior is divided into three Gothic naves.
The main choir begins in the transept with a Renaissance altar built by order of Bishop Mateo de Burgos. In the transept is the Chapel of Saint Liberata (Librada), the female patron saint of the city, with a splendid reredos and the relics of the saint, all constructed at the expense of Bishop Fadrique de Portugal, who is buried there.
What is now the Chapel of St. Catherine was dedicated to St. Thomas of Canterbury by the English Bishop Jocelin, who came to Spain in the party of Queen Leonora. What draws most people to the chapel nowadays is the sepulchre of Martín Vázquez de Arce (Martin Vasques de Arze in the spelling of the time). Vázquez died during the conquest of Granada and his brother Fernando, bishop of the Canary islands, ordered a portrait in alabaster where he lies on his side while reading in one of the finest examples of Spanish funerary art. It contrasts with the lying figures of his parents in the same chapel. The authors of the Spanish Generation of 1898 (Ortega y Gasset) drew attention to this statue naming him el doncel de Sigüenza, "the boy of Sigüenza", but Vázquez left a widow and children. Cardinal Mendoza is interred in the main choir. Beyond the choir proper, which is situated in the centre, there is the sumptuous altar of Nuestra Señora la Mayor, in black marble from Calatorao and red marble, featuring spiral Solomonic columns.
The main sacristy is also named as "of the heads". It was projected in 1532 by Alonso de Covarrubias and build by Francisco de Baeza and Martín de Vandoma. The portal is Renaissance, Plateresque, of 1573, in stone, the nuttree door has also Plateresque carvings and was damaged by a cat door and the Napoleonic troops. The half cannon vault features 304 big heads, all different, and 2000 smaller ones, hence the nickname of the room.
The ceiling and the vitrals of the cathedral were damaged in the Spanish Civil War, with the reconstruction ending in 1947. Connected with the cathedral is a beautiful Florid Gothic cloister, the work of Bernardino de Carvajal. The rich tabernacle, with its golden monstrance, was given by Cardinal Mendoza. The chapter house contains many excellent paintings. It is not known with any certainty at what period this church was begun, though it appears to date from the end of the twelfth century. The image of Nuestra Señora la Mayor, to whom the church is dedicated, dates from the end of the twelfth century; it was taken to the retro-choir in the fifteenth century, the Assumption being substituted for it on the high altar.
The Conciliar Seminary of San Bartolomé is the work of Bishop Bartolomé Santos de Risoba (1651). There is a smaller seminary, that of the Immaculate Conception, and a college. The College of San Antonio el Grande is a beautiful building. It was formerly a university (see below), founded in 1476 by the wealthy Juan López de Medina, archdeacon of Almazán, but its prosperity was hindered by the foundation of the University of Alcalá; in 1770 it was reduced to a few chairs of philosophy and theology, until it was suppressed in 1837.
The castle is now a Parador, a state-run luxury hotel.
Worthy of mention are the ancient hermitage of Nuestra Señora, which according to tradition was originally the pro-cathedral; the Humilladero, a small Gothic hermitage, now a tourism office; the Churrigueresque convent of the Franciscans; the modern convent of the Ursulines, which was formerly the home of the choir boys; the hospital of the military barracks; and the Hieronymite college.
Among the professors were the mathematician and theologian Pedro Ciruelo, who enhanced the prestige of the university as a center of learning; Don Francisco Delgado, Bishop of Lugo and rector, under whom the university reached its period of greatest splendor; Don Fernando Velosillo, rector and professor, who was sent by king Philip II of Spain to the Council of Trent; also present at that council were, as theologians, Don Antonio Torres, first Bishop of the Canary Islands, and Señor Torro, both professors of this university; Don Pedro Guerrero, Archbishop of Granada; the famous Cuesta; Tricio and Francisco Alvárez, Bishop of Sigüenza. Thus evidently the influence of the University of Sigüenza in the Spanish Catholic church and kingdom was considerable in the last years of the fifteenth century and the first years of the sixteenth; thereafter it fell into decay. It was suppressed in 1837.