The principal early building material of civilization was brick, most often unfired. Even thousands of years before civilization, builders in Jericho used sun-dried mud brick, sometimes called pisé. Adobe is a somewhat better sun-dried brick made from clay reinforced with straw. Adobe brick was also commonly used in Old World cities. Fired brick was usually reserved for public buildings or for facing structures of sun-dried brick.
Brick, especially unfired, weathers away quickly. As a result, the best known architecture of ancient times was of stone, the material of choice for temples, palaces, and other large public buildings. Stonehenge and the limestone pyramids and sphinx of Egypt offer the principal images of truly ancient structures, followed in our minds (although much later in fact) by the marble temples of Greece, the marble amphitheaters and baths of the Roman Empire, and yet more limestone-faced pyramids in Mesoamerica.
Simple structures of giant stones arranged in a pattern are called megaliths. The megaliths that were erected across the western European continent, on Great Britain, and on Malta include tombs (called dolmens), temples, and observatories. Similar groups of erect giant stones were constructed as tombs in India and other places in Asia thousands of years later. From a technological point of view, quarrying, moving, and erecting the stones, which often weighed 40 tons or more, seemed to be beyond the abilities of Neolithic or Bronze Age farmers. Diffusionist theories of the past called for Minoan or Egyptian engineers, but it is now clear that the megalith builders came earlier than the Minoans and that some of the monuments predate Egyptian engineering. The megalith builders used fire to make cracks in stone, which they then split using the power of swelling of wet wood along with progressively larger wedges. Lacking wheeled vehicles, it is thought that they simply dragged the stones, perhaps with the aid of sledges, or sometimes floated them partway on rafts. An inclined plane and a predug hole helped set the stones upright. For the most part, these were the same techniques used by the Egyptians in building the pyramids, but the megalith builders probably discovered the methods independently.
The rulers of Mesopotamia did not have stones to work with. Nevertheless, they built tall structures reaching toward the heavens. Called ziggurats, these temple towers were made from brick, often cemented together with tar (bitumen) or tar mixed with sand and gravel (mastic). In the absence of other, cheaper materials, molten lead could have been used as mortar. Sun-dried brick and adobe were usually cemented with more of the same mud that had been used to make the bricks. If limestone or gypsum was present, it could have been heated and then ground to form lime plaster or cement that hardens when water is added, similar to the mortar used by today's masons. Lime plaster was used in ancient Egypt and by most early civilizations of both the Old and New Worlds.
Egyptian engineers and early temple builders in South America often dressed stones so that they fit tightly together, shaping them so that gravity held them in place. The megalith builders who put up the last stage at Stonehenge used a version of this method, quarrying the stones so that they could dovetail mortises and tenons, forming rigid joints. Greek architects and early Romans also used iron cramps (right-angled bars) to hold stones in place.
Sometime around the third century bce the Romans began to use volcanic ash found in Italy, notably huge beds near Puteoli (Pozzuoli) on the Bay of Naples. These had been produced during eruptions of Mt. Vesuvius. Ground ash could be added to lime mortar to produce cement as hard as rock, cement that hardened even underwater. The silica in the ash combined with the calcium carbonate of the lime and with the water. By the early Roman Empire the new form of cement, mixed with sand and rock to form concrete, had become the principal building material, almost as cheap as brick and often better than stone. Although the Roman builders never abandoned stone and brick completely, they used more and more concrete and less and less stone and brick. Often the stone or brick ceased to have a structural purpose and was used as ornamentation for the concrete walls of buildings.
