A manuscript rather obliquely named from its once having been at Rosslyn Castle, but that at the time of this edition had come to the Advocates' Library at Edinburgh, which since 1925 is part of the National Library of Scotland (MS Advocates 18.5.19). Lawlor dated it to the late 13th or early 14th century, and saw it as an English copy of an Irish exemplar in turn descended from a book belonging to the Benedictine nuns of St Werbugh, Chester, in the 12th century.