Olivier Messiaen (1908–1992), undoubtedly one of the most influential composers of the 20th century and certainly the most important in the field of organ music of this era, wrote his eighteen-movement Livre du Saint Sacrement in 1984/85. In a way, this last and most extensive organ composition represents the sum of his musical language - modes with limited transposition possibilities, serial procedures of time and pitch organization, birdsong, quotations from Gregorian chants, Ancient Greek verse metres, and Indian rhythms as well as the "langage communicable" invented by the composer himself are used to represent theological ideas within the framework of the mosaic-like formal structures so characteristic of Messiaen. Conceptually, the Livre du Saint Sacrement revolves around the Catholic idea of the incarnation of Christ in the form of bread and wine.