Theodore Spandounes (or Spandugnino) belonged to a Byzantine refugee family who had settled in Venice after the Ottoman conquest of Constantinople in 1453. He wrote an account of the origins of the Turkish rulers and of their phenomenal rise to power. It was partly a plea to the Popes and princes of western Christendom to unite against the infidel, and was one of the earliest works of its kind. The first version of the book, written in Italian, appeared in 1509 and was translated into French in 1519. The final version was made in 1538, and a full Italian text was published in 1890, though without any historical commentary. This book presents an English translation of the full text with a preface, commentary and notes; a discussion of the sources which Spandounes might have consulted; and an assessment of the value and interest of this hitherto neglected and undervalued treatise.