Even as late as the middle of the thirteenth century little advance seems to have been made in Europe, for one of the most curious phenomena of the crusades was the improvement in the health of the army of Saint Louis after it surrendered. During the campaign various epidemics had been very fatal; but when the soldiers were subjected to the sanitary regulations of the Egyptian medical staff, disease disappeared. The Arabs had a strong taste for mathematics, and were familiar with most of the discoveries which have been attributed to astronomers of the fifteenth and sixteenth centuries. As early as 1000 spherical trigonometry was in use, and Aboul-Hassan wrote an excellent treatise on conic sections. In 833 the Caliph El-Mamoun, having founded observatories at Bagdad and Damascus, caused a degree to be measured on the plain of Palmyra. By the thirteenth century the Arabic instruments were comparatively perfect. They had the astrolabe, the gnomon, the sextant, and the mariner’s compass, and Aboul-Wafa determined the third lunar variation six hundred years before Tycho Brahe. To enumerate all the improvements in agriculture and manufactures which came from the mediæval pilgrimage would take a separate treatise. A French savant thought of writing a book upon the flora of the crusades alone. The mulberry and the silkworm were brought from Greece, the maize from Turkey, the plum from Damascus, the eschalot from Ascalon, and the windmills with which, down to the present century, corn was ground, were one of the importations from the Levant. It might almost be said that all the West knew of the arts was learned on the road to the sepulchre. The Tyrians taught the Sicilians to refine sugar, and the Venetians to make glass; Damascus steel was a proverb, Damascus potters were the masters of the potters of France; the silk, brocades, and carpets of Syria and Persia were in the twelfth century what they have been down to the present day, at once the admiration and despair of Western weavers, while there can be little doubt that gunpowder was the invention of the chemists of the East. All the evidence tends to prove that the ogive came from the Levant, and without the ogive Gothic architecture could never have developed.[107] Prior to the council of Clermont the pointed arch was practically unknown west of the Adriatic; but the Arabs had long used it, and it may still be seen in the ninth century mosque of Teyloun.