The Altar Declaration is a term used to describe a set of three documents that were signed in the early 16th century. The first document, the ARA, was signed by the Spanish Crown and the Catholic Monarchs, Isabella I of Castile and Ferdinand II of Aragon. This document declared that all religious services should be conducted according to the Roman Catholic faith. The second document, the APSE, was signed by the Pope and declared that the Spanish Crown had the right to appoint bishops and other religious officials. Finally, the IDO was signed by the Spanish Crown and declared that all religious services should be conducted in Latin. Together, these documents formed the Altar Declaration, which established the Roman Catholic Church as the official religion of Spain.