In any case, the oracular events during festivals provided an opportunity for people to receive responses from the normally isolated deities, as did the other varieties of oracle that developed late in Egyptian history. Temples eventually became a venue for yet another type of divine contact: dreams. The Egyptians saw dreaming as a means of communion with the divine realm, and by the Ptolemaic period many temples provided buildings for ritual incubation. People slept in these buildings in hopes of contacting the temple god. The petitioners often sought a magical solution to sickness or infertility. At other times they sought an answer to a question, receiving the answer through a dream rather than an oracle. After their original religious activities ceased, Egyptian temples suffered slow decay. Many were defaced by Christians trying to erase the remnants of ancient Egyptian religion. Some temple buildings, such as the "mammisi" at Dendera or the hypostyle hall at Philae, were adapted into churches or other types of buildings. Most commonly the sites were left disused, as at the Temple of Khnum at Elephantine, while locals carried off their stones to serve as material for new buildings. The dismantling of temples for stone continued well into modern times. Limestone was especially useful as a source of lime, so temples built of limestone were almost all dismantled. Sandstone temples, found mostly in Upper Egypt, were more likely to survive. What humans left intact was still subject to natural weathering. Temples in desert areas could be partly covered by drifts of sand, while those near the Nile, particularly in Lower Egypt, were often buried under layers of river-borne silt. Thus, some major temple sites like Memphis were reduced to ruin, while many temples far from the Nile and centers of population remained mostly intact. With the understanding of the hieroglyphic script lost, the information about Egyptian culture that was preserved in the surviving temples lay incomprehensible to the world. The situation changed dramatically with the French campaign in Egypt and Syria in 1798, which brought with it a corps of scholars to examine the surviving ancient monuments. The results of their study inspired a fascination with ancient Egypt throughout Europe. In the early nineteenth century, growing numbers of Europeans traveled to Egypt, both to see the ancient monuments and to collect Egyptian antiquities. Many temple artifacts, from small objects to enormous obelisks, were removed by outside governments and private collectors. This wave of Egyptomania resulted in the rediscovery of temple sites such as Abu Simbel, but artifacts and even whole temples were often treated with great carelessness.