During the years we call the Dark Ages (500 to 1300 A.D.), Europe was in a semi-barbarous state and there was little learning outside of the monasteries. All the culture and advances made by the Greeks and Romans seemed in danger of perishing in the raids and attacks of barbarous tribes, and wars among the early European peoples. But the Arabs, on whom we look today as almost barbarians, were the highly cultured race of that far-off time. They were great mathematicians and from them we have Algebra and our Arabic numerals 1, 2, 3, 4, etc. From them we have the arabesques, or the intricate geometric designs in carvings and traceries, seen on buildings in the countries where the Arabs built, lived, roamed or studied. Long before the Christian era there were very wonderful Arabian universities in Bagdad and Damascus, so famous that they attracted many Greek and Hebrew scholars to learn from the Arabian philosophers and wise men. Mohammed, their greatest prophet, who was born in 570 A.D., wrote their holy book called the _Koran_. While he lived the Arabs were at the height of their power. Because they had studied the learning of the past, and had invaded and conquered parts of Europe, the Arabs brought to Europe their arts and sciences and the learning of the ancient nations. Through their conquests they also carried their ways of living into the countries of the barbarians. For example, in 711, they drove the Goths out from Spain and set up their own caliphs (rulers) in that country, so that at this time they had two capitals—the original Bagdad and one at Cordova. From these Arabs, who came from Mauretania in Africa to Spain, descended the people we call Moors. It is for this reason that we have traces of Arab music and the Moorish architecture or Arab-like buildings of which the Alhambra is best known, in Spain. In Cordova, grew up a center of learning, far greater than any in the surrounding countries. At the university was a library of over 600,000 manuscripts not yet in book form, for printing had not been invented. Here, too, great chemists studied and discovered alcohol, sulphuric and nitric acids. The clock also was invented by the Arabs, and the game of chess was first thought out when the Chinese were already playing Mah Jong! They were responsible, too, for trigonometry as well as algebra, and they knew how to make cotton goods, and were famous for the Damascus steel out of which the swords of the heroes for many generations were forged. Even today Damascus steel is looked upon as excellent. As they were worshippers of Mohammed, they were not permitted to make portraits of human beings in stone or on parchments for they believed that they would be deprived of their souls at the day of judgment should they reproduce the human form. So they put their artistic efforts into color and design.