It is therefore scarcely possible to say that a specifically Mohammadan art existed during the first century after the Flight, though its germs were latent in the welding together of Hellenized with un-Hellenized, or barely Hellenized, regions under a single hand. The architecture of the first century gives evidence of the formative character of this process of compression; before the third century had ended it may be said to have been completed. If the monuments of the first century are still a faithful reflection of earlier and foreign creations, they hold the promise of further and more definitely characterized growth. But in an age and in lands where change was slow-footed, older conceptions continued to hold the field long after the political conditions under which they had arisen had vanished or had been baptized with other names. As we now know, the Mesopotamian palace builders of the ninth century of our era were guided by schemes which their Sasanian forerunners had inherited from remoter times; while the mosque builders had advanced little beyond the plan laid down in the camp-cities of the conquest. But the interchange of workmen between East and West was continuous, the intercourse unbroken; and from that intercourse, coupled with the needs of the age and the prejudices of the Faith, the arts of Islâm were born. In the present study my eyes have been turned chiefly, and necessarily, backwards. I have not been so much concerned with the offspring as with the parentage of the buildings which I have passed under review. Of these buildings the most important is the great palace of Ukhaiḍir on the eastern side of the Syrian desert. I have given, also, the first plans and photographs of three small ruins in its vicinity, Qṣair, Mudjḍah, and ‘Aṭshân. If they do not belong to the same period as the palace, they cannot be far removed from it in date. The problems presented by Ukhaiḍir led me back to Sasanian architecture, and I publish here new plans and photographs of two vast constructions at Qaṣr-i-Shîrîn. I have, further, taken this occasion to publish the plans of two mosques, the one at Diyârbekr, the other at Mayâfârqîn, both of which belong to a later period. The first of these has been known to us only through a sketch made by Texier, which I found to be inaccurate in many significant points, as it is also incomplete. The second has not previously been studied.