De mensura orbis terrae

De mensura orbis terrae (Concerning the Measurement of the World) is a work completed in 825 CE by Dicuil, an Irish monk, grammarian, and geographer. This text is significant for its contributions to the history of science and demonstrates the learning present in Ireland during the 9th century.1

Dicuil's work includes the earliest known mention of Irish hermits visiting Iceland in 795 CE, where they observed the midnight sun. It also contains a definite Western reference to the ancient freshwater canal connecting the Nile River to the Red Sea, which was noted as being blocked up in 767 CE. Dicuil learned of this canal from another Irish monk, Brother Fidelis, who had sailed along the Nile into the Red Sea and passed the Pyramids of Giza. Dicuil's writings also cite numerous Greek and Latin authors, as well as his contemporary, the poet Sedulius.1