The unwritten record of history is preserved in buildings in temples, fortresses, sanctuaries, and cities constructed of brick and stone. Early efforts to build permanent shelter were limited to the materials at hand. The trees of a primeval forest, the clay and mud of a river valley, the rocks, caves, and cliffs of a mountain range afforded only primitive opportunity for protection, security, and defense and few examples survive. But the stone and brick of skeletal architectural remains date as far back as the temples of Ur built in 3000 B.C., the early walls of Jericho of 8000 B.C., and the vaulted tombs at Mycenae of the fourteenth century B.C. It was the permanence and durability of the masonry which safeguarded this prehistoric record of achievements, and preserved through centuries of war and natural disaster the traces of human development from cave dweller to city builder. Indeed, the history of civilization is the history of its architecture, and the history of architecture is the history of masonry.