Anyone interested in medieval liturgical music will not want to miss the collection of music manuscripts kept at the Abbey Library of St. Gall. It was at the Abbey that neume notation was brought to perfection. Neume notation was an early medieval system of musical notation, the first in which the complete range of Gregorian chant melodies was written down. The Abbey was also home to the monks Notker Balbulus (around 912), the master of the sequence, and Tuotilo (around 913), who perfected the trope. As far back as the Middle Ages, music needed to be based on theory. The texts on music theory exhibited here date from the 6th to the sixteenth century. They cover a wide spectrum: from texts on music as a mathematical science to teaching about the key system and church modes to a short treatise in verse form on the art of conducting. Also during the Renaissance and until well into the eighteenth century, a large number of music manuscripts were produced at the abbey; others found their way into the Abbey Library collection as part of the estate of the Swiss historian Aegidius Tschudi. On display are some four-part vocal pieces written by the Italian composer Manfred Barbarini Lupus in 1562, Renaissance songbooks with sacred and secular compositions, manuscripts of the St. Gall cathedral organist Fridolin Sicher (1490-1546), a richly decorated antiphonary (one of the last manuscripts to be produced at the abbey), a composition by the St. Gall monk Maurus Christen (1747-1812), printed arias from the printing press of the Abbey of St. Gall and a transcription of a Mozart symphony – albeit dating from after the dissolution of the abbey.