Biographical details for earlier historical figures can be maddeningly elusive. Leonel Power, an English musician who was, with John Dunstaple, arguably seminal for the development of all European classical music, lived a life many details of which remain shrouded in the mists of time. Power's biographers can only guess at his birth date based upon the style of his music, and can only narrow it down to the 15-year span 1370-1385. (One earlier historian had proposed a birth many years before that, with a birthplace in Ireland's Waterford County, but was almost certainly incorrect.) The first documentary record of his life comes from 1419, when Power was registered as a leading chaplain in the retinue of Thomas, Duke of Clarence (younger brother of King Henry V). In 1423 he was in Canterbury, entering the fraternity of Christ Church; by 1439 at the latest he was serving that church as choirmaster. It is otherwise difficult to pinpoint his activities from the death of his patron the Duke in battle (1421), and Power's presence in the service of John, Duke of Bedford from 1439-1444; it is entirely possible that he immediately moved to Bedford's chapel. A good friend of Power's also apparently served Clarence with him, was nephew to Bedford's chamberlain, and could have offered Power a conduit in the old boy's network for such a new job. His death date of June 6, 1445, in Canterbury is well-attested. Power lived and worked in a time of great cross-fertilization and change in European music. While the late fourteenth century had been a period in which French music crossed the channel to Britain, in the first few decades of the fifteenth, English music and musicians were influential on the Continent. Many English musicians are known to have been present among the international convention of the Council of Constance, as well as traveling with their English patrons on campaigns such as Harfleur and Agincourt (or in occupied France afterwards). And Leonel Power was one of the most prominent among them. The important manuscript known as "Old Hall" was probably compiled for the chapel of the Duke of Clarence, but was later associated with the royal chapels of both Henry V and Henry VI (Henry V composed a piece of music within it). Power wrote possibly three times as much music as any other known composer in Old Hall, and his theoretical treatise "on the gamme [gamut, or musical scale]" was also well-known.