Volume XX 1513-1521, Leo X, Lateran Registers Part One. This volume is part of a series of calendars of entries in the papal registers of out letters in the Vatican Archives. It covers the first tranche of the chancery, or Lateran registers, of Leo X (1513-21) and brings to light a great mass of biographical and topographical information illustrating the ecclesiastical landscape of Great Britain and Ireland at a critical moment. The letters imply a constant traffic between the British Isles and the Curia and provide valuable insights into relations between the national churches and the papacy in the run-up to the break with Rome. These are essential background papers of the Reformation.