One thousand years ago, Islam was the most followed religion of a great expanse of territory stretching from Spain and North Africa in the West to the borders of China in the East. In the Islamic world, there were three caliphates namely, the Umayyads of Spain, the Fatimids of Egypt and the Abbasids of Iraq, in the 10th century CE. The 10th century CE was considered to be a golden era for the Spanish city of Cordoba which became the vital centre of learning in the Islamic West. The caliphs of Cordoba repeatedly had friendly relations with Orthodox Christian Byzantium (Constantinople or Istanbul) at the opposite end of the Mediterranean Sea. Since the wealth of the Spanish Umayyads increased, their Great Mosque in Cordoba was expanded and made even more beautiful. True story of a unique example of cooperation between the Byzantine emperor in Constantinople and the Spanish caliph in Cordoba which led to the building of the most beautiful Mihrab in the world! has been discussed in this book.