This article focuses on the decline of Spanish ecclesiastical music from the beginning of the 19th century, coinciding with the outbreak of the War of Independence. This decline worsened as a result of the application of successive disentailments by the various liberal governments and the signing of the Concordat of 1851. To remedy this situation, various reform projects and initiatives were proposed by authors such as Eslava, Barbieri, Pedrell and Olmeda, with the ultimate aim of revitalising religious music in Spain and the musical chapels that supported it: such projects, which gained considerable momentum thanks to the Cecilianist movement, were the prologue to the promulgation of the Motu Proprio by Pope Pius X in 1903.