DICUIL (fl. 825), Irish geographer, is only known by his work, ‘Liber de Mensurâ Orbis terræ.’ That he was an Irishman by birth, if not by residence, is proved by his phrases, ‘heremitæ ex nostra Scottia navigantes’ (p. 44), and ‘circum nostram insulam Hiberniam’ (p. 41); for Scottia was not used as the equivalent of the modern Scotland till a century after Dicuil's time at the very earliest. In the same direction tends his accurate knowledge of the islands near Britain and Ireland, ‘in alias quibus ipsarum habitavi, alias intravi, alias tantum vidi, alias legi’ (p. 41). On the other hand it has been plausibly maintained that he was a member of one of the numerous Irish monasteries that in his days still flourished in different parts of the Frankish empire (Wright, i. 372, &c.). This theory may perhaps be supported by his allusion to the Gallic poet Sedulius, ‘auctoritate aliorum poetarum et maxime Virgilii, quem in talibus causis noster simulavit Sedulius, qui in heroicis carminibus,’ &c.; but hardly on the lines of Wright's argument that ‘only within the bounds of Charles's empire could he have found copies of the authors whom he quotes.’ Even in the phrase just cited it is not unlikely that Dicuil uses the ‘noster’ for the sake of supporting the practice of a heathen poet like Virgil by that of ‘our own’ christian epic ‘poet Sedulius,’ and not as token of community of race.
From Dicuil's ‘Liber de Mensurâ’ we learn that he was a pupil of a certain Suibneus, ‘cui, si profeci quicquid, post Deum imputo’ (p. 25), in whose presence our author heard brother Fidelis describe his pilgrimage to the Pyramids and Jerusalem. This Suibneus Letronne has attempted to identify with a Suibhne whose death the Irish annals assign to 776 A.D., and on this somewhat slender foundation proceeds to argue along a chain of inferences to the conclusion that Dicuil was born between 755 and 760 A.D. Dicuil himself he tentatively identifies with a Dichullus, abbot of Pahlacht, whose date the Irish annals do not indicate (Letronne, Prolegom. pp. 23–5). Accepting these dates, Dicuil must have been from thirty-five to forty years old when in 795 A.D. he received the visit of the clerks who had spent six months in Iceland (Liber de Mens. pp. 42–4). It has been surmised that he was in France during the lifetime of the great elephant sent by Haroun Al Raschid to Charlemagne. If this surmise were true, he must have been there between the years 802 and 810 A.D., the date of the animal's arrival at Aix and its death; but there is nothing in Dicuil's own phrase to imply that he himself saw the elephant, but rather the contrary (Liber de Mens. p. 55; Letronne, pp. 150–2). Of the other details of his life we are ignorant, except that in 825 A.D.,
Post octingentos viginti quinque peractos
Summi annos Domini terræ ethræ carceris atri,
he completed his only remaining work, the ‘Liber de Mensurâ Orbis terræ,’ after he had already issued an ‘Epistola de quæstionibus decem artis grammaticæ,’ now lost (Liber de Mens. pp. 1, 85).
The ‘Liber de Mensurâ’ is a short treatise on the geography of the world. It professes to be based on a survey of the world, ordered and carried out by the Emperor Theodosius in the fifteenth year of his consulship or the fifteenth of his reign. It is uncertain whether the Theodosius alluded to is Theodosius I or II. Dicuil's latest editor (Parthey, pp. xii–xiii) seems to incline to Theodosius II; but that our author attributed the survey to Theodosius I appears evident by his use of the words ‘Sanctus Theodosius imperator.’ Dicuil's work is divided into nine sections: (1) Europe, (2) Asia, (3) Africa, (4) Egypt and Ethiopia, (5) on the length and breadth of the world, (6) on the five great rivers, &c., (7) on certain islands, (8) on the breadth and length of the Tyrrhene Sea, (9) on the six (highest) mountains. Of these sections the first five are derived from the Theodosian survey, which he chose for the basis of his work, because, though vitiated by false manuscripts, it was less faulty than Pliny, especially in its measurements. The last books are mostly excerpts from Pliny, Solinus, and Isidore; with, however, interesting additions of his own when touching on the Pyramids and the Nile, on the islands round Britain and Ireland, on Iceland (Thile), and a few other places. These additions he derived from the trustworthy accounts of certain, possibly Irish, monks who had visited these lands. Specially interesting is his story of Fidelis's adventure near the Pyramids, where the narrator saw the corpses of eight men and women lying on the desert sand, all slain by a lion who lay dead beside them; and the account of the Iceland nights at the summer solstice, which were so bright that a man could see to do what he would ‘vel peduculos de camisia abstrahere tamquam in præsentia solis’ (pp. 26, 42–3). The first of these passages is relied on by Letronne for fixing the time of Dicuil's birth; for Fidelis, the narrator, had journeyed in a ship along the canal connecting the Nile with the Red Sea; and as this canal is known to have been blocked up by Abou Giafar Almansor in 967 the voyage of Fidelis must have been anterior to this (see Letronne, Proleg. 10–22). Dicuil was a cautious writer, especially as regards statistics. From this spirit he left blank spaces in which his readers might insert the length of rivers where he could not trust the figures of Pliny or of Theodosius's missi. This system has produced some surprising results, e.g., where the length of the Tiber is put at 495 miles, and that of the Tagus at 302; or where the Jordan is reckoned 722 miles long, and the Ganges only 453 (Liber de Mens. pp. 4, 31, 36, 38). Dicuil also draws upon certain works now lost, e.g. a ‘Cosmography’ (‘nuper in meas manus veniens’), drawn up under the consulship of Julius Cæsar and Mark Antony (ib. pp. 28, 36, &c.; but cf. Bunbury, Hist. of Ancient Geogr. pp. 177–9, 693, 701); and a ‘Chorografia’ drawn up by command of Augustus (p. 5). The list of authors from whom he borrows is very large, including, in addition to those already mentioned, Virgil, Orosius, and Servius (pp. 68, 72, 81); but Hecatæus, Homer, Herodotus, and other Greek writers he seems always to refer to at second hand (pp. 22, 46, 78; for a full list see Parthey's Preface, pp. vi and vii).
The ‘Liber de Mensurâ’ was first printed as a whole by Walckenaer (Paris, 1807); next, with copious prolegomena, historical and geographical, by Letronne (Paris, 1814). Lastly, the text has been carefully edited and furnished with a minute index and a short critical preface, by Gust. Parthey (Berlin, 1870). There are two manuscripts belonging to the tenth century or thereabouts, viz., one at Dresden (Regius D. 182), another at Paris (Biblioth. Nation. 4806); of these the first forms the basis of Parthey's edition, the second that of Walckenaer's and Letronne's. Other but later manuscripts are to be found at Venice (fifteenth century), Oxford, Rome, Vienna, Munich, and Cambridge.[Prefaces to Parthey's and Walckenaer's editions; Hardy's Biog. Literaria, i.]