Bricks

The Indus valley
The humble brick literally shaped the face of world architecture. The Nile, Tigris-Euphrates, and Indus River valleys were the locations of what has been calledthe urban implosion, the sudden emergence of cities from the neolithic villages that lined the waterways. The alluvial expanses on whose agricultural produce the new urban centers burgeoned had little naturally occurring stone, so the city walls, the buildings within, and even the royal palaces were built of brick. Packed clay had been used for centuries, and as it does in parts of the Arab world today, it yielded soft, curvilinear free forms. The advantage of the brick was that it was a prefabricated modular building unit, made easy to handle by its size and weight. Its shape and standard sizefunctions of the manufacturing process inevitably generated a rectilinear architecture and affected the way people built by assembling units rather than allowing the building to grow as well as limiting such details as proportion and the subdivision of surfaces. Those causes and effects persist until this day. Sun-dried bricks were made from puddled clay, perhaps containing a little sand or gravel, reinforced with a fibrous material usually straw that minimized cracking as the bricks dried. The mixture was packed into wooden molds, without tops or bottoms, that were removed once initial hardening had occurred. The bricks were then stacked and left to dry in the sun, sometimes for as long as two years, before being used in buildings. They were usually set in beds of wet mud, although the ancient Egyptians are known to have used gypsum-based mortar. The Babylonians employed hot natural bitumen, imported from lakes at Id on the Iranian Plateau every several courses, the bed joints were reinforced with woven reeds. The dry climates of the river valleys presented few problems with weathering, but sometimes walls were plastered over with mud. The Indus valley culture employed kiln-fired bricks long before its contemporaries, in buildings, pavements, and drains. Fired bricks also appeared a little later in Mesopotamia, where they were employed only in such special situations as decorative facings with colored glazes of public buildings or copings on walls. Timber for building was in short enough supply, and it was unreasonable to use it unnecessarily to fuel kilns. In the land between the rivers, sophisticated brick technology was early applied to massive structures like King Ur-Nammus ziggurat at Ur ca. 2100 b.c.. It was mainly of sun-dried brick, with thick facings of fired brick. Sixteen centuries later the Babylonian king Nebuchadnezzar II built his new city, with an 11-mile-long 17-kilometer outer wall and an inner wall wide enough to allow two chariots to be driven abreast on its top. Both of these huge structures were of sun-dried brick, and the northern Ishtar Gate was faced with blue glazed brick, ornamented with colored brick relief figures of bulls, dragons, and other beasts. Nebuchadnezzar also refaced the Marduk zigguratthought by some to be the Tower of Babelwith a 50-foot-thick 15-meter fired brick casing. Because the successive cultures that later dominated the region were builders in stone, the value of brick architecture was overlooked for centuries, to appear again in the Roman world. For the pragmatic Romans, brick construction was more economical than stone, so the material was widely used, Brick making became a major industry that eventually was nationalized. To maintain quality control, brick makers were obliged to stamp their products with the brick makers name and the place and date of manufacture. Flat Roman bricks, laid in thick beds of lime mortar, were used to build arches and principally aslost formwork in the ubiquitous concrete structures, in which they were covered with marble, mosaic, or stucco. Although it was maintained as a decorative material in the Byzantine Empire, with the decline of the Western Roman Empire, brick again went out of fashion. For several centuries after about a.d. 400, the only bricks used in western Europe were recycled from Roman buildings. It was only when those supplies were exhausted by about the beginning of the twelfth century that brick was again revived. As had been the case in the protohistoric river civilizations, necessity gave birth to invention, and brick architecture reappeared in the stone-poor Low Countries. Trade routes through Flanders were integral to the spreading use of bricks and clay roof tiles as building materials, and they moved as trade goods or as ballast in ships. Even toward the end of the Middle Ages, English architects and their clients regarded the brick as an exotic, luxurious, and somewhat suspicious building material.