The cathedral-basilica of Nuestra Señora del Pilar or Santo Templo Metropolitano de Nuestra Señora del Pilar is one of the two metropolitan cathedrals of the archdiocese of Zaragoza, together with the Seo del Salvador, as well as a minor basilica. It is usually called simply "basilica del Pilar" or "el Pilar". It is an important Baroque temple dedicated to Our Lady of the Pilar in the city of Zaragoza (Aragon, Spain).

According to tradition, it is the first Marian temple in Christendom, since it preserves and venerates the pillar - in reality, a jasper column - which, according to tradition, was placed there by the Virgin Mary who, while still living in Jerusalem, appeared in mortal flesh to the Apostle James on 2 January 40. There is no documentary proof of what is recorded in the tradition, the details of which date from 1297 - in a papal bull by Pope Boniface VIII - and 1299 - a declaration by the Jurors of Zaragoza - where the dedication of "Santa María del Pilar" is attested for the first time, after Bishop Hugo de Mataplana undertook in 1293 to restore the building, which was in danger of ruin, thanks to donations made possible by the aforementioned papal bull.

The documented history of the church dates back to the 9th century, when, according to the Historia del traslado de San Vicente de Aimoino, there is evidence of the existence of a Mozarabic church in Saraqusta dedicated to Saint Mary, in the same place where the Baroque basilica now stands. One of the city's Christian communities was based around this church.

Architecturally, the basilica has three naves, of equal height, covered with barrel vaults, interspersed with domes and plate vaults resting on sturdy pillars. The exterior is made of brick, following the Aragonese brick construction tradition, and the interior is plastered with stucco. The central nave is divided by the presence of the main altar under the central dome, with the large altarpiece of the Assumption, belonging to the previous church, made by the sculptor Damián Forment in the 16th century. Under the other two elliptical domes of the central nave, there is the Santa Capilla de la Virgen del Pilar, and the choir and organ, which also came from the previous Gothic church. They have now been moved to the lower section of the church, to provide more space for the faithful who occupy the nave from the main altar.

El Pilar has held the rank of cathedral or seo since the Bull of Union of 1676, sharing since then the seat of the archbishop of Zaragoza with the neighbouring Seo del Salvador. In 1948, Pope Pius XII granted it the title of minor basilica.

The Basilica of El Pilar, together with the sanctuaries of Torreciudad, Montserrat, Meritxell and Lourdes make up the Marian Route, an itinerary guided by Marian spirituality and devotion, with a great wealth of heritage, gastronomy and nature. Since 2007, it has also been one of the 12 Treasures of Spain.