At Roger’s instigation and with his aid Al-Idrīsī, or Edrisi (as the name is more usually written), who had come to the Sicilian court from Spain, undertook a great series of geographical labors. Little is known of the life of Edrisi besides a few details to be gleaned from later biographers[338] and what he himself tells us in the preface to his _Geography_, as it is usually known, or, to cite its Arabic title, _The Recreation for Him Who Wishes to Travel Through the Countries_, which was completed in 1154 or later.[339] We know that he constructed for Roger a celestial sphere and a disk-shaped map of the world, both of silver. Furthermore, we are told that Roger provided him with special facilities for the construction of maps and for the compilation of his great treatise. It appears that the king and Edrisi together selected “certain intelligent men, who were despatched on travels and were accompanied by draftsmen. Just as soon as these men returned Edrisi inserted in his treatise the information which was thus communicated to him.” On the basis of observations made in the field, data derived from Ptolemy and earlier Arabic geographers were correlated and brought up to date. The book and the maps which were drawn to elucidate the book are for this reason unquestionably among the most interesting monuments of Arabic geography; furthermore, the book is the most voluminous and detailed geographical work written in twelfth-century Europe. After a very brief description of the earth as a globe, the hemispheres, climates, seas, and gulfs, Edrisi launches into a long and minute account of the regions of the earth’s surface. He takes up the seven climates in order, dividing each climate into ten sections, an arrangement that is artificial to excess. None the less, Edrisi’s works are of exceptional quality when considered in comparison with other geographical writings of their period, partly by reason of their richness of detail but mainly because of the scientific method used, the coöperative employment of many observers, and the critical correlation of their observations—a procedure which was indeed unlike that adopted by Latin scholars of the time. INFLUENCE OF SICILO-MOSLEM GEOGRAPHY The question of the full extent to which the fruits of this Sicilian geographical school became known in the Latin Europe of the late twelfth and early thirteenth centuries is a matter that awaits further investigation. Certainly the influence of Edrisi’s _Geography_ could not have been great in the world of letters or else traces of it would more easily be detected in Western literature. Unlike a multitude of Arabic writings of far less intrinsic value, the _Rogerian Description_ (as the _Geography_ of Edrisi is often called) found no Gerard of Cremona to put it into Latin, and the authoritative geographical knowledge of the Western world was destined to develop unenriched by the treasures which Roger and Edrisi together had amassed.