The earliest written records of the Welsh harpists' repertoire are contained in the Robert ap Huw manuscript, which documents 30 ancient harp pieces that make up a fragment of the lost repertoire of the medieval Welsh bards. The music was composed between the 14th and 16th centuries, transmitted orally, then written down in a unique tablature and later copied in the early 17th century. This manuscript contains the earliest body of harp music from anywhere in Europe and is one of the key sources of early Welsh music. The manuscript has been the source of a long-running effort to accurately decipher the music it encodes.