"When the players have played the music through once, they repeat it, only this time, the lead violinist, known as the first violinist, adds extra notes to embellish the melody. Such embellishments would often have been made up on the spot--improvised. Indeed, much of the instrumental music of the Renaissance was improvised. Leonardo da Vinci, the great Italian inventor and painter, was also a fine musician, but he never wrote his music down, he simply made it up on the spot. Improvisation, unfortunately, is no longer a part of Classical music--improvisation in Classical music started disappearing in the nineteenth century."
-- based on Listen, by Kerman
