The Leiden choirbooks are six volumes of polyphonic renaissance music of the Franco-Flemish school preserved in the Pieterskerk, Leiden. The books were compiled for the Pieterskerk's College of the Seven Liturgical Hours, a professional choir employed at the Pieterskerk, as at many large Dutch city churches during the 15th Century, to sing masses for the dead - or rather those of the dead rich enough to have had left bequests and endowments for masses to be sung for them. Leiden was the first city to acquire a professional college for these masses, c.1440. Rotterdam, Delft in both churches, Haarlem, Gouda, Alkmaar, and finally Amsterdam (as late as 1468) also set up dedicated "college" choirs.