The church of San Andrés is a Romanesque temple with three naves and two apses. The first corresponds to the central nave, while the second is a later addition in which the sacristy is located. The lateral naves are the old porticoed atriums that were inserted in the temple during the Baroque period. The nave of the gospel houses the chapel of the San Gregorio. The nave of the epistle has at its feet the baptistery and at its head the chapel of San Sebastián (today called the Sagrada Familia). This is the lower body of the graceful Romanesque tower made by Mudejar master builders. Said tower and the apses are what give the church its characteristic and identifying aspect, both in its surrounding square and in the profile of the city.

The construction of the parish must have begun before the year 1120. This data derives from the fact that on this date the first indirect allusion to the temple appears, when speaking of a gate in the wall called San Andrés. Only the main apse, made of stone, remains of the original 12th-century temple. The current body of the naves, as well as the tower correspond to a later intervention carried out during the 13th century by Mudejar master builders who enlarged the church using brick.
 

Finally, in 1604, the last notable intervention of the building's structure began, carried out by Sebastián González, Juan Setién, Martín de Mendizábal and Andrés Rodríguez. This consisted of the closure of the porticoed atriums for the extension of the temple (which correspond to the current lateral naves), as well as the Baroque restoration of all its internal space. The set of all this performance was long and intermittent, and culminated with the celebration of the Feast of the Fourteenth of the year 1664.