Dicuil

Dicuilus (or the more vernacular version of the name Dicuil) was an Irish monk and geographer, born during the second half of the 8th century.

The exact dates of Dicuil's birth and death are unknown. Of his life nothing is known except that he belonged probably to one of the numerous Irish monasteries of the Frankish Kingdom, became acquainted, by personal observation, with islands near England and Scotland. From 814 and 816 Dicuil taught in one of the schools of Louis the Pious, where he wrote an astronomical work, and in 825 a geographical work.

Dicuil’s reading was wide; he quotes from, or refers to, thirty Greek and Latin writers, including the classical Homer, Hecataeus, Herodotus, Thucydides, Virgil, Pliny and King Juba, the late classical Solinus, the patristic St Isidore and Orosius, and his contemporary the Irish poet Sedulius. In particular, he professes to utilize the alleged surveys of the Roman world executed by order of Julius Caesar, Augustus and Theodosius II.

The astronomical work is a sort of computus of four books, in prose and verse, preserved only in a manuscript which belonged formerly to the monastery of Saint-Amand in northern France, and is now at Valenciennes.

Book 1 contains material on calendars, on 19 year lunar cycles, and on versification. It also contains an account of the two methods of calculating triangular numbers: by summation of the natural numbers, or by the multiplication together of two consecutive numbers divided by two.

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