The Arch-Building of Santa María is among the most emblematic monuments of Burgos. It is mentioned in the Epic Poem of El Mío Cid. At the time of the great Castilian hero, it was the most famous of the twelve doorways to the town. Through it passed Rodrigo Díaz de Vivar when he left Burgos to fight the Moors and when he came home to rest from the bloody battle. Its present appearance dates back to the second third of the 16 C.
Juan de Vallejo and Francisco de Colonia renovated the building following the design of a stately castle, with two robust round towers and a triumphal arch in memory to Carlos V.
In the Arch-Building are represented, apart from Carlos V, important persons of Medieval Castile: the two main judges, Laín Calvo and Nuño Rasura; the founder of Burgos, Count Diego Porcelos; the first independent count, Fernán González; and El Cid Campeador.
Inside is the Room in Purity or Secret Room, where the Council of Burgos used to meet until 1791. It is covered by a beautiful Mudéjar coffering from the 14 C. The room displays a collection of items related to the Cid, such as a bone of his body, along with an authenticity document, a reproduction of the Tizona sword and a facsimile of the edition of the Poem of Mio Cid. The collection also includes the armchair of the judges of Castile, the Vara of Burgos or Castile, a unit of length popularised by Felipe II, the key of the castle of Burgos and the Brazier and the Doorway to the Archives of the building.
In the 1990´s the interior of the building was meticulously restored. Between the years 1879 and 1955, it was occupied by the Archeological Museum. In 1994 it reopened its doors, and today the monument houses the Historical-Artistic Cultural Centre of Burgos.