During the Dark Ages period, the Islamic world was making great advancements in science and math. They were using translated Greek and other ancient texts to build on where they left off. A Persian astronomer and mathematician al-Khwarizmi developed algebra. Some Islamic art uses geometric patterns and symmetries, such as girih (strapwork lines) tiling. In 1424, geometric patterns were used in the archway of the Sultan’s lodge in the Ottoman Green Mosque in Bursa, Turkey. In the 11th century, another Islamic Mathematician, Ibn Muadh al-Jayyani, wrote The Book of Unknown Arcs of a Sphere. The law of sines is attributed to him. These are just a few examples of the progress the Islamic world made during the Middle Ages. It is also referred to as the Golden Age of Islam. Some historians believe these advances are better than the math and sciences advances that Western Europe made during the same time