The Arabs introduced the industrially manufactured paper of the orient instead of using the parchment or papyrus of the Romans. This greatly lowered the cost of books, and led to an increase in productivity, facilitating both literary and scientific studies. Although philosophy and astronomy were so strongly opposed by the common people and the priestly class of the Moslems that their study was at times forbidden by the government,[17] they were a fruitful topic in the education and researches of the upper classes. One of the greatest glories of Arabic civilization was the transmission of Greek culture to western Europe, for the Arabs had become acquainted with the works of the Greeks, while western Europe had almost completely forgotten them. Nevertheless, Moslem Spain was to be more important in this respect in the period following the downfall of the caliphate. Mathematics and medicine did not meet with popular and religious opposition, and in both of these sciences the Arabs achieved notable results. Polite literature, however, and especially poetry, was the most favored intellectual medium. Poetry had been cultivated by the Arabs while they were yet in their crude tribal stage. It was not unusual for challenges to personal combat or declarations of war to be written in poetry. Books of science, even, made their appearance in verse, and the improvisation of poetry was a general practice. The most favored subject-matter illustrates a pronounced trait in Arabic character, for amorous themes of an immoral order accorded best with Arabic taste. The Spanish Moslems were not notable in painting and sculpture, but distinguished themselves in architecture and the industrial arts. Perhaps the most important feature of their cultivation of these arts was the introduction of Byzantine influences. They made use of the dome and of the elaborate decoration of flat surfaces (especially of walls) with arabesques, so named because of their profuse employment in Arabic work. In addition they painted their buildings in brilliant and variegated colors. They rarely built in stone, preferring brick, plaster, and adobe. The mosque was the principal example of their architecture. In that and in their civil edifices they made use of one feature, not unlike that of the Roman house, which has survived in Spain,--the enclosed court, or _patio_, surrounded by arcades, with a fountain in the centre. Streets were narrow, both with a view to provide shade against the heat of the sun, and also because of the necessities of space, so that the city might be contained within its walls. CHAPTER VI CHRISTIAN SPAIN IN THE MOSLEM PERIOD, 711-1035 [Sidenote: Fitful character of the Christian reconquest.]