One day, when he was 13, he was looking at some old music in a second-hand music shop. He found some very old music for solo cello. They were the "Cello Suites" by Bach. People in those days thought they were just a collection of studies to help cellists with their technique, but Casals, although only still a boy, realized it was great music. He spent the next 12 years practising them until he felt ready to perform them. Casals’ discovery of these wonderful Cello Suites was the most important Bach discovery since 1829 when Mendelssohn found and performed the St Matthew Passion which the world had forgotten about.