Architecture is the art of enclosing space for some human purpose. In ancient Greece the "master builder" supervised the construction of temples and other public buildings. From his title in Greek, architekton, comes our word, "architect." Nowadays an architect must receive a great deal of scientific training in practical matters having to do with his profession. He must know mathematics, as well as many facts concerning materials — for example, what loads different materials may safely carry — so that there will be no danger of his buildings falling down. Another part of an architect's education is concerned with the principles underlying beauty. We call these "aesthetic principles." They have to do with the elements that are shared by all the line, shape, space, light, and color, controlled by pattern, balance, rhythm, contrast, and unity. With these principles and with his scientific knowledge, the architect creates useful structures that give us pleasure, a sense of the beautiful. A fine building, then, is firmly constructed of good materials and serves its purpose well, while at the same time it gives us a feeling of beauty that is similar to the feelings we have when we hear music or enjoy painting and sculpture. As we shall see in looking at some of the noted buildings of the past and present, architects are free to emphasize either of the two aspects of their art, sometimes the structural, sometimes the aesthetic, but most often they skillfully combine both aspects. Let us look first at a renowned example of the art of architecture, the famous tomb known as the Taj Mahal.