In the sphere of the arts and crafts, our best evidence lies in architecture and engineering. In these the Arabs had no skill and were conscious of their incapacity. The earliest mosques were simply enclosures surrounded by a plain wall, but a new type was developed under the first `Umayyad Khalif Mu`awiya, who employed Persian non-Muslim builders in the construction of the mosque at Kufa, and they worked on the lines of the architecture already used by the Sasanid kings. In this mosque the traditional square enclosure was retained, but the quadrangle was surrounded by a cloister in the form of a collonade with pillars 30 cubits high of stone drums held together by iron clamps and lead beddings. From this the cloistered quadrangle became the general type of the congregational mosque and remained so until late Turkish times, when it was partly superseded by the Byzantine domed church. The dome had been used in earlier times only as the covering of a tomb, standing alone or attached to a mosque. The same Khalif Mu`awiya employed bricks and mortar in restorations which he made at Mecca, and introduced Persian workmen to execute the repairs. In 124 A.H. (A.D. 700) the fifth `Umayyad Khalif found it necessary to repair the damage caused at Mecca by flood, and for this purpose employed a Christian architect from Syria. In the time of the next Khalif al-Walid, the “Old Mosque” of Fustat (Cairo), that is now known as the “Mosque of `Amr,” was rebuilt by the architect Yahya b. Hanzala, who probably was a Persian. The earlier mosque had been a simple enclosure. The next oldest mosque of Cairo, that of Ibn Tulun (A.H. 283) also had a non-Muslim architect, the Christian Ibn Katib al-Fargani. Not only in the earlier period, but also in the days of the Abbasids, the Muslims relied exclusively upon Greek and Persian, to a less degree on Coptic, architects, engineers, and craftsmen for building and decoration. In Spain of the 2nd century (8th century A.D.) we find the Byzantine Emperor sending a mosaic worker and 320 quintals of tessarae for the adorning of the great mosque at Cordova.