When Jesuit missionaries first arrived in what is now eastern Bolivia at the end of the 17th century, they found the indigenous peoples of the area to be musically inclined and taught them to sing, to make and play fiddles, harps, wind instruments and such, and to compose music in a hybrid European-South American idiom. Reporter Nicholas Casey travels to the old mission and cathedral town of Concepción to find that the tradition of music-making has remained strong – and that, to the amazement of musicologists, thousands of scores from the 18th century have survived there and even remained in use.