History of Ireland is a fragment of a voluminous work Engels intended to write and on which he worked at the end of 1869 and during the first half of 1870. Engels studied a vast selection of literary and historical sources: the works of antique and medieval writers, annals, collections of ancient law codes, legislative acts and legal treatises, folklore, travellers’ notes, numerous works on archaeology, history, economics, geography, geology, etc. Engels’s bibliography, embracing over 150 titles, is selective and includes but a fraction of the sources he studied.