Spanning over three thousand years, ancient Egypt was not one stable civilization but in constant change and upheaval, commonly split into periods by historians. Likewise, ancient Egyptian architecture is not one style, but a set of styles differing over time but with some commonalities. The best known example of ancient Egyptian architecture are the Egyptian pyramids, while excavated temples, palaces, tombs, and fortresses have also been studied. Most buildings were built of locally available mud brick and limestone by paid laborers and craftsmen. Monumental buildings were built using the post and lintel method of construction. Many buildings were aligned astronomically. Columns were typically adorned with capitals decorated to resemble plants important to Egyptian civilization, such as the papyrus plant. Ancient Egyptian architectural motifs have influenced architecture elsewhere, reaching the wider world first during the Orientalizing period and again during the nineteenth-century Egyptomania. Characteristics Due to the scarcity of wood, the two predominant building materials used in ancient Egypt were sun-baked mud brick and stone, mainly limestone, but also sandstone and granite in considerable quantities. From the Old Kingdom onward, stone was generally reserved for tombs and temples, while bricks were used even for royal palaces, fortresses, the walls of temple precincts and towns, and for subsidiary buildings in temple complexes. The core of the pyramids consisted of locally quarried stone, mud bricks, sand or gravel. For the casing, stones were used that had to be transported from farther away, predominantly white limestone from Tura and red granite from upper Egypt. Ancient Egyptian houses were made out of mud collected from the damp banks of the Nile river. It was placed in moulds and left to dry in the hot sun to harden for use in construction. If the bricks were intended to be used in a royal tomb like a pyramid, the exterior bricks would also be finely chiselled and polished. Many Egyptian towns have disappeared because they were situated near the cultivated area of the Nile Valley and were flooded as the river bed slowly rose during the millennia, or the mud bricks and sun-dried brick of which they were built were used by peasants as fertilizer. Others are inaccessible, new buildings having been erected on ancient ones. However, the dry, hot climate of Egypt preserved some mud brick structures. Examples include the village Deir al-Madinah, the Middle Kingdom town at Kahun, and the fortresses at Buhen and Mirgissa.