ARAGON, constituent kingdom of the Spanish monarchy, administrative unit until 1833, now divided into the three prov inces of Saragossa, Huesca and Teruel (q.v.). The north frontier of Aragon follows the Pyrenean water-parting, from the peak of Anie (2,504m.), the last of the great peaks towards the west, to the peak of the Aneto (3,404m.) in the Maladetta group. Thus Aragon is backed by the western, or forward, echelon of the high Central Pyrenees, nearly to the point where the headwaters of the River Garonne separate it from the eastern. From this back ground of high peaks the descent to the lowlands of the Ebro is less rapid (average gradient 31 in loo) than the descent towards the Garonne on the French side (7 in zoo) . The difference is due to the much greater development on the south side of topo graphical features parallel to the principal axis of the chain. Thus the River Aragon—finding at Jaca the soft marl which runs from east to west in a belt from Pamplona, in Navarre, to diverted west and forms the broad valley of the Canal de Berdun; the influence of this belt is seen also in the course of the Cinca and of certain minor, streams. East of Boltana the rivers flow directly south, and the first of these, the Noguera Ribagorzane, gives the eastern boundary of Aragon. South of the belt of marl, a series of sierras—roughly aligned from west-north-west to east-south-east—of which the Sierra de Guara (2,o 7 om.) is the most important, runs from the River Ara gon to the Sierra del Montsech (1,693m.) in Catalonia ; these sierras overlook the great, saucer-shaped central lowland on their south, across which runs the River Ebro. The heart of Aragon is this lowland and more strictly that part to which the descent from the crest of the Pyrenees is most obviously a descent by steps. The approaches to the defile by which the Ebro cuts its way from this enclosed basin through the Catalan coastal chain to the sea belong to Catalonia from Fayon downstream. The western boundary of Aragon runs more or less diagonally across the sierras bordering the central plateau so as to include within Aragon, in the south, the greater part of the sierra belt, while in the north the commanding Sierra del Moncayo (2,315m.), im mediately overlooking the Ebro lowland, forms an advanced bulwark of Castile. The descent from the central plateau is again by steps, and the border of Aragon is defined so as to cover the important structural depression, occupied in part by the River Jiloca, which runs from Calatayud, on the river Jalon, to Teruel. From the eastern limit of this depression the boundary runs to the Ebro at Fayon so as to include in Aragon the headwaters of the streams flowing to the Mediterranean. It is clear from the above that Aragon divides naturally into zones, parallel in the north to the Pyrenees and in the south to the border of the plateau. In the first zone, that of the high Pyrenean valleys, cultivated patches sustain scanty village populations ; there is some mining —the cobalt mines are interesting—but the forest and the high summer pastures are the chief resources.
The next, the limestone zone to the south, includes picturesque scenic forms carved by the rivers; it is represented as high as the Pyrenean crest in the Monte Perdido (3,352m.), one of the Three Sisters group. The zone is of no economic importance, but its strategic interest is obvious from the structure. Behind the protecting sierras to the south, Sierra di Guara, etc., beyond which the Muslims made no lasting conquest or impression, sprang up early in the Muslim period the countships of Aragon, with centre at Jaca, Sobrarbe, with centre at Ainsa, and Riba gorza, at first forming a single fief with Pallas. Until its estab lishment gs an autonomous fief in 875, Ribagorza-Pallas was de pendent on Toulouse through Cerdagne, and the influence of the easy Segre-Cerdagne pass across the Pyrenees extended as far westwards as the Esera, the western boundary of Ribagorza. The separation of Pallas, the amalgamation (between 1034 and 1038) of Ribagorza with the western countships, which had always looked west to Navarre, and the declaration of Aragon as an in dependent kingdom (c. 1034) defined the boundaries of Upper Aragon as described above.
The lowland zone, which dips from an altitude of 500m. to the Ebro (at Zoom. near Saragossa) and rises again to the south towards the sierras, is by no means uniform. The frequency of local regional names, Monegros, Desierto de Calanda, Llano de Violada, indicates variations which express themselves some times in the nature of the soil (especially in the presence or absence of gypsum), but principally in the presence or absence of a non-brackish water-supply. Huesca, in the north of the zone, on the old road from the coast by Lerida which, to-day as always, avoids the arid, waterless plateau of Los Monegros, was an important town long bef ore Saragossa, the natural centre of the lowlands. In the period following the final establishment by Augustus of Roman authority in the entire peninsula and with the new appreciation of the importance of the line of the Ebro as a base-line in strategical schemes envisaging the peninsula as a whole, Saragossa became a most important nodal point of corn munications. Standing at the point of confluence with the Ebro of the Gallego valley, by which came the road from the Pyrenean pass of Summus Portia, and of the Huerva on the south, Sara gossa was also within 15 miles of the mouth of the Jalon, the en trance to the pass leading by the Sierra Ministra and the river Henares to the Tagus, and in Saragossa was focussed the im portance of the central lowland from which radiated all the routes to the interior of the peninsula. These advantages of site the city has always enjoyed, mutatis mutandis, in a degree corresponding with the degree of unification of the peninsular regions. The central lowland of Aragon had its most complete historical ex pression in the Muslim period as the kernel of the kingdom of Saragossa. Not always able to maintain its independence of the Umaiyads of Cordova or of the Moroccan dynasties controlling the south, nor able always to control the north of its own area where the cities had climatic advantages and where Huesca had a much older tradition, the kingdom did not long survive the capture by Aragon of Monzon (r o89) and of Huesca (1o96) ; Saragossa itself fell in III 8. The union of the enlarged kingdom of Aragon, now centred in Saragossa, with the maritime state of Catalonia (1135) gave it a new Mediterranean outlook. The circumscription of Aragon by Castile both on the north, where the district of La Rioja and the plateau of Soria became finally Castilian, and on the south, where the conquest of Murcia for Castile drove a wedge between Valencia, held by the Aragonese, and the Muslims of Granada, forced eastwards the expansion of Aragon and led to the foundation of the Aragonese empire, for which see general article on Spain.
The southern part of Aragon would form one single zone of hill country were it not for the strip of sheltered valleys along the line of the Jalon and of the depression marked by the towns of Calatayud, Daroca and Teruel. With Albarracin, on the upper Guadalaviar, these towns formed the four communities which dominated the hill pastures for many centuries. The peach ripens in the valleys, where the irrigated lands are intensely cultivated; apart from these the sheep pastures on the hills are the principal resource.
In temperature Lower Aragon is intermediate between that of Old Castile with its low mean winter temperatures and that of New Castile with its high mean summer temperatures. North ward from the Sierra de Guara the seasons are reduced more and more to long severe winters and short cool summers; in a lesser degree the same is true of the highlands of Aragon. The rainfall is small save on the Pyrenean front, and we note the approximate equality both of the winter and summer minima and of the spring and autumn maxima. The deficiency of the rainfall, which does not exceed 50omm. annually over the greater part of Aragon, and falls below 3oomm. in the neighbourhood of Saragossa, has made irrigation a prime necessity. For irrigation conditions are less favourable than they appear at first sight to be if one con siders only the schematic arrangement of lowland with surround ing hills and mountains and thp apparent abundance of the water supply in the rivers. This ideal schema is discounted by the un favourable conditions of relief and of soil, which have made the provision of canals proper, as opposed to mere trenches, imper ative for irrigation, and by the extreme seasonal variation in the rivers, to meet which schemes are now in progress for the con struction of enormous dams on their upper courses. Large capital expenditure under State leadership has made irrigation in Aragon a political question ; the phrase politica hidrdulica was coined here to describe the impassioned campaigns of Joaquin Costa (1846-1911) on its behalf. In the most recent times a new and wider conception of the whole problem of irrigation in the north east has led to the establishment by royal decree (March 5, 1926), of the Con f ederacion Sindical Hidrogrdfica del Ebro with head quarters in Saragossa, which grew from a scheme for a reservoir at Reinosa, province of Santander, of capacity 550,000,000 cubic metres to regulate the Ebro. The indirect social and political consequences of assembling round one table delegates from Castile, the Basque Provinces, Navarre, Aragon and Catalonia for vital economic business may be even greater than the direct economic consequences of a unified irrigation policy. Of the canals the most important are the Imperial canal (96 kilos in length with 2 kilos of annexes), with intake from the Ebro on the right bank below Tudila and terminating at El Burgo, below Saragossa; the Canal de Tauste (342 kilos), on the opposite side of the river; the Canal de Aragon y Cataluna, with intake from the 1? sera near Olvena, the principal canal terminating near the junction of the rivers Segre and Cinca. The largest reservoir is that of La Pena, on the River Gallego, with a capacity of 25,000,000 cubic metres. The Moneva reservoir, on the River Aguas, with a capacity of i r,000,000 cubic metres, is the largest in south Aragon. These figures are dwarfed by those of the proposed new reservoirs and canals. Besides the Reinosa reservoir mentioned above, those of Sotonera on the Gallego and of El Mediano on the Cinca enormously exceed in capacity any existing reservoir; they form part of a scheme for the irrigation of Upper Aragon, which includes the construction of a canal 146 kilos in length for the irrigation of Los Monegros, a canal which, if constructed, will be the longest in Europe after the Cavour canal, in Italy. BIBLIOGRAPHY.-M. Serrano y Sanz, Noticias y Documentos histo ricos del Condado de Ribagorza (1912) ; R. B. Merriman, Rise of the Spanish Empire, vol. i. book II. (1918), with bibliographical appendix to each chapter ; R. Menendez Pidal, Origenes del Espanol (1926) .