year (the spring equinox in March). Book 4 contains material on solar intercalary days and lunar subtracted days; and on the relative speed of travel of the moon, sun and stars. De mensura Orbis terrae Better known is the De mensura Orbis terrae, a summary of geography, giving concise information about various lands. This work was based upon a Mensuratio orbis prepared by order of Emperor Theodosius II (AD 435), a manuscript copy of which was possessed by the Carolingian court. Godescalc had already made use of this copy (781-783) for the composition of his celebrated Evangelistarium. Dicuil uses Pliny the Elder, Gaius Julius Solinus, Paulus Orosius, Isidore of Seville, and other authors, and adds the results of his own investigations. In the nine sections he treats successively of Europe, Asia, Africa, Egypt, and Ethiopia, the area of the Earth's surface, the five great rivers, certain islands, the length and breadth of the Tyrrhenian Sea, and the six (highest) mountains. Although mainly a compilation, this work is not without value. Dicuil is our only source for detailed information of the surveys performed by order of Theodosius II; his quotations, generally exact, are of service for the textual criticism of the authors mentioned; of great interest, too, are the few reports which he got from the travellers of his time; as, for instance, from the monk Fidelis who (possibly in 762 CE) journeyed along the canal then still existing, between the River Nile and the Red Sea; and from clerics who had visited the Faroe Islands and lived possibly in Iceland for six months during the summer of 795. Among their claims are the perpetual day at midsummer in "Thule," where there was then "no darkness to hinder one from doing what one would." They also described navigating the sea north of Iceland on their first arrival, and found it ice-free for one day's sail. Editions The geography manuscript was known to Marcus Welser, Isaac Vossius, Claudius Salmasius, Jean Hardouin, and Johann Daniel Schöpflin; it was first printed with the title: Dicuili Liber de mensura orbis terrae ex duobus codd. mss. bibliothecae imperialis nunc primum in lucem editus a Car. Athan. Walckenaer (Paris, 1807). J. J. Tierney, Dicuil: Liber de Mensura Orbis Terrae, (Dublin 1967). Notes References Irish Christian monks Irish explorers 9th-century Irish poets 8th-century Irish writers 9th-century Irish writers 9th-century Latin writers Irish astronomers Irish expatriates in France Irish