After the Romans annexed the Kingdom of the Nabateans in 106, the area experienced a building boom that lasted until the onset of strife and instability in the mid-3rd century. Though the Romans greatly influenced the region's architecture, the Hauran's Nabatean inhabitants largely maintained their own building traditions, particularly in the smaller towns. The architecture of the Byzantine era was influenced by the spread of Christianity and the consequent construction of churches and monasteries, the majority dating between the 4th century and early 6th century. Surveys of the region indicated that a long period of uninterrupted building activity took place in the Hauran between the Nabatean period in the 1st century to the Umayyad period in the 7th century. The region's pre-Islamic architectural tradition became the basis for later Islamic buildings in the Hauran, particularly in Bosra in the 12th–14th centuries. However, the Muslim patrons of these works also introduced outside elements, mostly inspired by Damascene architecture, to give their projects their own stately character. Archaeology The Hauran is distinguished by the large-scale preservation of its ancient structures. This preservation extends to public and religious buildings, but also to simpler structures, such as village dwellings. The durability of basalt is generally credited with their well-preserved state. As a result, there are some 300 towns and villages in the Hauran containing ancient structures, almost as high a concentration as the Dead Cities of northwestern Syria. In the words of 20th-century archaeologist Howard Crosby Butler, There is no other country in the world where the architectural monuments of antiquity have been preserved in such large numbers, in such perfection, and in so many varieties as in North Central Syria [the Dead Cities] and in the Hauran. There are many places where the minor details of buildings, such as wall-paintings and mosaics, are in a better state of preservation; but there is no [other] region where numbers of towns of undoubted antiquity stand unburied, and still preserving their public and private buildings and their tombs in such a condition that, in many cases, they could be restored, with a small outlay, to their original state. When Classical-era sites were largely resettled in the late Ottoman era, many of the Hauran's ancient monuments were converted into houses. Surveys The earliest surveys of the Hauran's archaeological sites were taken in the 19th century by the French archaeologist Melchior de Vogüé between 1865 and 1877, S.