What inexpensive building material is the key to the future of architecture? Take a guess in the comments. Find the answer below. . . . . . Soil, or earth, is a building material that's easily obtainable, environmentally sustainable, and seemingly in infinite supply. Although this modest material has been used in construction for millennia, people often think of it as something found solely in developing countries—but this is far from true. Consider the beautiful neighborhoods of Santa Fe, New Mexico, old and new, made of mud brick. The oldest public building in the United States still in use is the Palace of the Governors in Santa Fe, built in 1610 and today part of the New Mexico History Museum. The walls of the Alhambra Palace in Granada, Spain, are largely constructed of rammed earth; the palace's name, from the Arabic Al Hamra, meaning red, refers to the color reflected by earthen walls at sunset. In Mali, the Old Towns of Djenné, including the Great Mosque, are made from ear...