Dicuil (Dícuil(l))
In the same year he also wrote two other works, of which unquestionably the most important is his treatise on geography, ‘Liber de mensura orbis terrae’, which is arguably the best book on geography from the early middle ages. Dicuil used a wide range of sources for this treatise, some of them now lost or only partly preserved, such as the ‘Cosmographia’ of Julius Caesar in the recension of Julius Honorius, as well as some derivative of the emperor Agrippa's map of the world, probably that known as the ‘Diuisio [or ‘Mensuratio'] orbis’ of Emperor Theodosius. Among his other sources are Pliny, Solinus, and Isidore of Seville. He had clearly spent some time in the islands north of Britain and Ireland to which he refers (vii, §6) as follows: ‘Near the island Britannia are many islands, some large, some small, and some of medium size. Some of them are situated to the south and west, but the majority are to the north-west and north. I have lived in some of them and I have visited others; some I have only glimpsed, while others I have only read about.’
It seems that Dicuil acquired his geographical knowledge of the islands around Britain from some time spent as a monk on Iona. He relates that he was present when a monk who had returned from a pilgrimage to the Holy Land, sometime before 767, was received by Suibne on Iona; it is likely that the ‘master Suibne’ to whom Dicuil refers was Suibne (qv) (d. 772), abbot of Iona 767–72. Dicuil draws on first-hand oral and written sources for his account of the settlement of Iceland and the northernmost islands of Britain by Irishmen in the eighth century. His descriptions of Egypt and Palestine are largely derived from written accounts, though he also refers to oral information picked up from a traveller which became the basis for one of the earliest descriptions in western literature of a crocodile on the river Nile. The date of his death is not known.