The Missa sopra Ecco sì beato giorno is a musical setting of the Ordinary of the Mass, for 40 and 60 voices, by Florentine Renaissance composer Alessandro Striggio. It probably dates from 1565–6, during the reign of his employer Cosimo I de' Medici. Lost for more than 400 years, it was recently rediscovered in Paris. Most of the mass is for five separate choirs of 8 voices each, with the closing Agnus Dei being for five separate choirs of 12 voices each; all of the voice parts are fully independent. With its huge polychoral forces, climaxing on sixty fully independent parts, it is the largest known polyphonic composition from the entire era.