It is uncertain whether the Missa Solemnis in C major was composed by Wolfgang Amadeus Mozart or by his father Leopold. Whatever the case, it was extremely popular during the 18th and early 19th centuries, and was performed by Simon Mayr who copied the score around 1802. Mayr’s own festive Te Deum is believed to have been written for Napoleon’s coronation as King of Italy in Milan Cathedral on 26 May 1805. Mayr’s biographer Girolamo Calvi praised this effective work in the highest terms, declaring it a masterpiece.