Chapter III: The Contribution of the Moslems

There is no necessity here of giving a general review of the very broad field of Arabic geography. The works of the foremost Mohammedan geographers, Al-Masʿūdī, Ibn Ḥauqal, Al-Iṣṭakhrī, were unknown in Europe during the Middle Ages, and formal Arabic geography certainly contributed next to nothing to the knowledge of the earth possessed by the Occidentals of the Crusading age.

_SOURCES_

Other branches of Arabic science, however, profoundly influenced the development of European thought at this time. As transmitters of classical learning to the West, the Saracens reintroduced fragments of the geographical lore of the Greeks. The two classical authors in whom they had taken the deepest interest were Aristotle and Ptolemy. Their most important contribution to Western geographical knowledge was to make known to the West geographical speculations in the works of these men and in the various treatises which the Moslem writers themselves had composed under Peripatetic and Ptolemaic influences.

INFLUENCE OF ARISTOTLE

Aristotle held a position of preëminent authority among the Moslems in all matters scientific. Arabic scholars had received his writings both through Syriac translations and direct from Greek texts. Vast commentaries on his works were made by Avicenna (Ibn Sīnā, 980–1037 A. D.) in the Eastern Caliphate and by Averroës (Ibn Rushd, 1126–1198 A. D.) in Spain. Aristotelian astronomy, as distinguished from Ptolemaic, was reproduced with modifications in the work _On the Sphere_ of Al-Biṭrūjī of Cordova, known to the Christians as Alpetragius.[323] By the end of the twelfth century, owing to the rising interest in Aristotelianism in Europe (the “flood of Aristotelianism,” as Duhem calls it), translations had been done from the Arabic into Latin of a large number of Aristotelian works on astronomy, physics, meteorology, and many other subjects.[324] It was in these works that most of Aristotle’s thought and observation in geography had found expression. Aristotelian physical geography, transmitted through these channels, was destined to dominate the geographical speculations of many Christian writers of the thirteenth century.

INFLUENCE OF PTOLEMY’S “ALMAGEST”

The Moslems of the Eastern Caliphate also had become familiar with Ptolemy’s _Almagest_ and _Geography_ through Syriac translations and through versions of the original Greek text.[325] A manuscript of the _Kitāb al-Majisṭī_, or _Almagest_, was translated into Arabic in the days of Hārūn ar-Rashīd by that caliph’s vizier, Yaḥyā, and other translations appeared during the middle part of the ninth century. Study of the _Almagest_ stimulated Arabic scholars and incited them to write such original treatises of their own as Al-Farghānī’s (Alfraganus’) On the _Elements of Astronomy_, Al-Battānī’s _On the Movements of the Stars_, or _Astronomy_,[326] and Ibn Yūnūs’ _Ḥakīmī Tables_.

INFLUENCE OF PTOLEMY’S “GEOGRAPHY”

Furthermore, Ptolemy’s _Geography_ was certainly known to the Moslems in Syriac translations and probably also in copies of the original Greek text.[327] With the _Geography_ as a model a number of Arabic treatises, usually entitled _Kitāb ṣūrat al-arḍ_, or _Book of the Description of the Earth_, were composed at an early period of Islam and served as bases on which later geographical writers built more complex systems. One of the most significant was the _Kitāb ṣūrat al-arḍ_ of Al-Khwārizmī, composed about the time of Al-Maʾmūn (813–833 A. D.), the full text of which was discovered forty-four years ago by Spitta.[328] From another book of the same sort and title Al-Battānī derived the geographical details included in his _Astronomy_.[329] The latter was translated into Latin during the twelfth century; and Al-Khwārizmī’s work was known in Europe at second hand.[330]

AZ-ZARQALĪ AND THE “TOLEDO TABLES”

Ptolemy was studied in the western as well as in the eastern centers of Islam. Toledo, notwithstanding its conquest by the kings of Castile in 1085, long remained a scientific center, where the Arabic spirit of investigation lingered on among Jew, Christian, and Moor. It was largely through Spanish channels that the Latin West found its Oriental inspiration in astronomy and astrology.[331] About 1080 Az-Zarqalī, of Toledo,[332] who had devised a new type of astrolabe, wrote various works on astronomical subjects, including a commentary on a series of astronomical tables that had been constructed by a group of Jewish and Moslem scholars before his time.[333] These so-called _Toledo Tables_, with Az-Zarqalī’s _Canons_ explaining them, contained some incidental geographical information derived in part from Ptolemy’s _Geography_ and from Al-Khwārizmī.[334] They were rendered into Latin in the twelfth century by the famous Gerard of Cremona, who probably found in Spain most of the manuscripts from which he made his many Latin translations.[335]

GEOGRAPHY IN SICILY

Ptolemy’s _Geography_ was also studied in Sicily under the Moslem emirs and their successors, the Norman kings. From the eleventh century date several Arabic descriptions of Sicily now known only in fragments but bearing eloquent witness to a true enthusiasm for geography prevalent among the Moslem aristocracy of the island.[336] The Normans, who became masters of Sicily between 1060 and 1071, preserved much that was best of Arabic traditions and culture, and Moslem scholars played a brilliant part in the intellectual life of the court. Roger II himself was a devotee of geography, occupying much of his spare time in collecting Arabic geographical treatises and in questioning travelers about distant parts of the earth. “He gave himself up to this work tirelessly for fifteen years, never ceasing to examine personally into all geographical questions, to search for their solution and to verify facts, in order that he might obtain in complete form all the information that he desired” (from Jaubert’s translation of Edrisi).[337]

EDRISI

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.

On the other hand, there is no question but that the Sicilo-Norman enthusiasm for geography exerted an indirect influence on the evolution of geographical knowledge, an influence that was to make itself felt more especially after the close of our period. This enthusiasm for geography was the product of a mingling of Arabic scientific and scholarly traditions with Norman maritime enterprise in an island which occupied a central position in relation to the world of its day. It was an enthusiasm that arose partly from pure love of knowledge but also in very large degree from the practical necessities of a sea-faring people, and it was early applied to the solution of the problems of navigation. In the words of De La Roncière, “The use of coast charts was destined to become general in Sicily; a rational method of navigation to be substituted for the routine of pilotage, and thus the way was prepared for the progressive conquest of the world.”[340] As De La Roncière goes on to point out, the Genoese learned the arts of navigation from the Sicilians in the early thirteenth century and transmitted them subsequently to the Spaniards, Portuguese, French, and English; and a new science of the sea was developed upon the foundations originally laid by Sicilian Moslems and Normans.[341]

ORIENTAL IDEAS TRANSMITTED TO THE WEST

Besides the classical heritage, the Moslems also transmitted some peculiarly Oriental ideas to the West. Al-Khwārizmī was the author of a treatise with astronomical tables, the translation of which by Adelard of Bath usually goes under the name of _Khorazmian Tables_.[342] The original work was a redaction of a book drawn ultimately from Hindu sources and known as the _Little Sindhind_.[343] Thus it was from Hindu sources, as is shown by this work, that the Mohammedans got their idea of the world center of Arin. Hindu religion, furthermore, contributed something toward the molding of Greek and Moslem doctrines of the periodicity of the universe and of the Great Year—doctrines which became widely known in the West through Hermann the Dalmatian’s Latin translation of the Persian Abū Maʿshar’s book, _The Great Book of the Introduction_, entitled in the Latin, _Liber introductorius in astrologiam_.[344] Hindu influences were also felt in an anonymous but widely read Arabic treatise falsely attributed to Aristotle in the Middle Ages and called _Liber de proprietatibus elementorum_.[345]

_ASTRONOMICAL GEOGRAPHY; THEORIES OF THE TIDES_

Turning now from the sources to the material substance of the contribution of the Moslems, we find that, except in so far as it brought a knowledge of Aristotle to Europe, it added little to Western notions either of physical or of regional geography. Though the Moslems entirely failed to share with the Western World their wide practical acquaintance with lands and seas, the Arabic writers did nevertheless introduce some new ideas in the fields of astronomical—or, better, astrological—geography and in the closely allied study of tidal phenomena.

THE GREAT YEARS

The theory of the Great Years was very popular among the Orientals, possibly because it appealed to their fatalistic spirit. Arabic astronomers adopted Ptolemy’s calculation of the length of the Great Year at 36,000 terrestrial years[346] and seem to have believed that after every complete revolution of the sphere of the fixed stars, the planets, as well as the fixed stars, will find themselves in the same relative positions that they held at the beginning of the revolution.[347] The Arabic work on this subject most read in the Latin West was Hermann the Dalmatian’s translation of Abū Maʿshar’s book, in which it was explained that astral influences—especially the perpetual circulation of the fixed stars—are the cause of everything which is born and dies and of everything which occurs between birth and death on this earth.

COSMIC CYCLES AND GEOGRAPHICAL CHANGES

In much the same way that the Chaldeans, Hindus, and Greeks had done, the Moslems worked out a theory of the supposed influence of these cosmic cycles on geography.[348] The most striking elaboration of the theory was made by the “Brothers of Piety and Sincerity,” who formed a philosophical school in the tenth century after Christ. In the great encyclopedic work[349] produced by this school (which, incidentally, contains many other interesting speculations on the subject of physical geography) gradual alterations in the relative position of land and sea are ascribed to almost imperceptible changes in the longitude of the fixed stars resulting from the precession of the equinoxes. Not only do lands and seas change places, but various types of terrain; in the course of time “cultivated land becomes desert, desert becomes cultivated land, steppes become seas, and seas become steppes or mountains.”[350]

Whereas this curious theory was accepted by the Aristotelian Al-Biṭrūjī, the author of the pseudo-Aristotelian _Liber de proprietatibus elementorum_ vigorously opposed to it the following argument.[351] If the fixed stars revolve around the earth in 36,000 years, the land ought to revolve around the 34,000 miles which he believed make the circumference of the earth in the same time, or, as we may infer, at a rate of slightly less than a mile per year. We should therefore expect to find certain cities much nearer the coast and other cities farther from the coast than they used to be. The anonymous author says that if the theory were valid one ought to be able to observe great changes in the position of such places as Arin, Ceylon, Byzantium, and Rome in relation to the sea. But since, as a matter of fact, no such changes are apparent, the whole theory of the transposition of land and sea falls to the ground.

Obvious as it may seem to us, this reasoning is remarkable at a time when actual observation as a foundation for, or check on, theorizing was rare indeed; and hence it is gratifying to note that the _Liber de proprietatibus elementorum_ with its argument against the Great Year, rather than the encyclopedia of the “Brothers of Piety and Sincerity” with its argument for it, was the work on this subject that was read by Occidental scholars.

THEORIES OF THE TIDES

The Moslems did not add much to the classical theories of the tides which they transmitted to Christendom. Their fundamental work concerning tides was that treatise of Abū Maʿshar which we have already mentioned, a work from which, as Duhem says, all the Middle Ages learned the laws of the ebb and flood.[352] Here, in the chapters on the moon,[353] a full description is given of the various characteristics of the tides together with copious speculations regarding their causes. The actual observations of fact were exact and careful. Abū Maʿshar explains with not a little accuracy the relation of the tides to the moon’s rising and setting, to her phases, and to the position of the sun; he understood that winds might cause exceptionally high water; he recognized the influences of local topographic features, that some seas display different tidal phenomena from others and that the flood waters may be retained by reefs, or valleys, or deep bays. On the other hand, Abū Maʿshar’s treatment of the causes of the tides was less successful. Though he believed firmly that the moon produces the ebb and flood, he failed to account for the presence of the high tide at the time of the moon’s opposition. His explanation of the moon’s attraction of the waters was in keeping with astrological methods of reasoning. Our satellite was supposed by astrologers to be of peculiarly aqueous nature and for that reason exceptionally capable of governing the movements of the liquid element of the earth.

Other theories of the tides entered the West from Arabic sources. Al-Biṭrūjī’s _On the Sphere_ ascribed their origin not to the moon but to the general circulation of the heavens.[354] Averroës, in a commentary on the _Meteorology_ of Aristotle, devoted a confused chapter[355] to an attempt at showing that ebb and flood are the results partly of currents produced by differences in level between the ocean and certain seas and partly of the moon’s attraction of the waters. The possibility of differences in level between seas and ocean had probably become known to the Spanish scholar through some garbled rendering of Eratosthenes’ observations on the currents and levels of the Mediterranean.[356]

MEASUREMENT OF A TERRESTRIAL DEGREE

That the Saracens also were interested in the more strictly mathematical aspects of astronomical geography is emphatically proved by the fact that they undertook actually to measure the length of a terrestrial degree[357] and thereby to determine the circumference of the earth. Some knowledge of this great work came to the Western world in our period through translations of the _Astronomy_ of Al-Farghānī.[358]

GEOGRAPHICAL POSITIONS

The Arabic investigations, however, which most profoundly interested the men of the West were those concerned with the determination of the location of places on the earth’s surface rather than those whose aim was to find the size of the globe. Stimulated by their interest in Ptolemy, the Moslems felt a special need for the accurate knowledge of positions, for upon such knowledge depended the construction of mosques, which, according to religious law, must face in the direction of Mecca. Astrology also necessitated this type of investigation. In order to cast a horoscope one must know what stars are overhead at a particular moment; and, to ascertain this, one must know latitude and longitude. In the Arabic astronomic works there occur rules for determining positions and tables of the latitudes and longitudes of places throughout the world.[359]

One of the most practical results of Arabic investigations in this field was a reduction of Ptolemy’s exaggerated estimate of the length of the Mediterranean Sea. The Greek geographer gave the length as 62° or about half again too long. Al-Khwārizmī cut this figure down to about 52°, and, if we are right in our interpretation of the available data, Az-Zarqalī still further reduced it to approximately the correct figure, 42°. As we shall see in a later chapter, the results of these corrections became known in the medieval West.[360]

The Moslems, as a general rule, measured longitudes from the prime meridian which Ptolemy had used, that of the Fortunate Islands (now the Canaries), situated in the Western Ocean at the westernmost limit of the habitable earth; but individual writers came to make use of another meridian farther west, a meridian destined to become known to the Christian world as that of the True West as distinguished from the supposed border of the habitable West.[361] Abū Maʿshar, on the other hand, referred his prime meridian to a fabulous castle of Kang-Diz, far to the east in the China Sea.[362]

ARIN

The western prime meridian was commonly supposed to be 90° from a mythical city called Arin (or Arim) situated on the equator, halfway between the farthest east and the farthest west. This city was said to have neither latitude nor longitude, and its meridian came arbitrarily to be placed at 10° east of that of Baghdad. The idea of Arin probably originated among the Hindus,[363] who believed that the city of Langka in Ceylon (or perhaps Sumatra)—the abode of devils—lies on the equator. They traced their prime meridian from Langka through Odjein, a place in India, to Mount Meru at the north pole—the abode of angels. Odjein was transliterated into Arabic as “Arin” or “Arim” and was shifted by the Moslems to the equator. It was made known to the Christian world through such works as Adelard of Bath’s translation of the _Khorazmian Tables_ (which, as we have already seen, was an Arabic redaction of a Hindu work) and Plato of Tivoli’s translation of Al-Battānī’s _Astronomy_. In the latter, Arin was represented as a cupola or tower; and on Christian maps and diagrams of the Middle Ages it was not infrequently so depicted.

_ARABIC EXPLORATION AND TRAVEL_

This sums up briefly a few of the more significant original ideas that the Moslems added to twelfth-century geographical knowledge in the West. By way of contrast, it is not out of place briefly to recall what they had actually accomplished in the field of geographical investigation.[364] Moslem trade between the seventh and ninth centuries reached China by sea and by land; southward it tapped the more distant coasts of Africa, including Zanzibar; northward it penetrated Russia;[365] westward Mohammedan navigators saw the unknown and dreaded waters of the Atlantic. Al-Masʿūdī speaks of the presence of Moslem traders in the heart of Europe, in a country to which he gave the name Ad-Dir (probably Bohemia).[366] Arabic literature abounds with descriptions of the lands within these wide borders; of their products and kingdoms and marvels, true and fanciful. But all this was destined to remain a sealed book to the man of the Latin Occident,[367] who as a rule felt little genuine interest in the world beyond his immediate ken. He looked to Arabic books for practical aid in making calendars and star tables and horoscopes; he looked to Arabic translations and commentaries on Aristotle for help toward a better understanding of the dark and hidden meaning in the words of Scripture. The geographical knowledge which he acquired from the Moslems during our period was merely incidental to other interests, a sort of flotsam borne in on the great wave of astrologic and Aristotelian lore sweeping into Europe at this time.