DICUIL (fi. 825), Irish monk, grammarian and geographer. His De mensura orbis terrae, finished in 825, contains the earliest notice of a European discovery of and settlement in Iceland and the most definite Western reference to the old fresh-water canal between the Nile and the Red sea, blocked up in 767. In 795 Irish hermits had visited Iceland, where they marvelled at the perpetual day of midsummer. Relics of their settlements were found by the permanent Scandinavian colonists of Iceland in the 9th century. Of the old Egyptian fresh-water canal Dicuil learnt from one "brother Fidelis," probably another Irish monk, who, on his way to Jerusalem, sailed along the "Nile" into the Red sea—passing on his way the "Bards of Joseph" or Pyramids of Giza, which are well described. Dicuil's reading was wide; he quotes from, or refers to, 3o Greek and Latin writers, the patristic St. Isidore and Orosius, and his contemporary the Irish poet Sedulius; he professes to utilize the alleged surveys of the Roman world executed by order of Julius Caesar, Augustus and Theodosius (whether Theodosius the Great or Theodosius II. is uncertain).
A short astronomical treatise written between A.D. 814 and 816 and dedicated to Louis le Debonnaire, the Frankish king in whose kingdom Dicuil was teaching, has been edited by Mario Esposito in the Proceedings of the Royal Irish Academy, vol. xxvi. s. C. (1907). Editions of the De Mensura were made by C. A. Walckenaer (Paris, 1907), A. Letronne (Paris, 1814) and G. Parthey (Berlin, 187o, best as to text). See also C. R. Beazley, Dawn of Modern Geography, vol. i. (1897).