contributions did Haydn and Mozart make to the classical era? Franz Joseph Haydn and Wolfgang Amadeus Mozart were other musical geniuses, this time contributing heavily to the classical era of music. Haydn composed 104 symphonies along with many string quartets, oratorios, Masses (like Bach), songs, and concerti. Another classical genius, Mozart was a child prodigy, writing his first opera at the age of twelve. He wrote such famous pieces as the operas The Marriage of Figaro, Don Giovanni, and The Magic Flute