All the great architectural forms were bound up, in their origin, with certain materials; and they never completely escape this limitation. The quarry gives us stone, the mine metals, the forest wood, the river bottom mud, and seashells or limestone will give us lime to make plaster. Here are the chief elements in all construction. What are their possibilities?

We hew and build the stone into walls or pillars and span the uprights with a stone laid flat across. That is post-and-lintel construction. It is the key to the simple, dignified architecture of ancient Egypt and Greece; in its development it gives us the temple at Karnak and the Parthenon, with the repetition of columns, the carefully studied horizontal and vertical lines, the mathematical proportions. If the space between the columns grows too wide for a single stone to span it, we must arrange a group of them together in an arch, so that one will hold the other in place; and if this load grows too heavy, we must reinforce the columns with buttresses, and balance thrust against thrust in a more complicated arrangement. When we push this mode of building to the limit, we have the fourteenth century French cathedral. As the shape of the building varies, we get characteristic ways of enclosing the roof - the flat roof, the dome, the gable. The form will depend largely upon the purpose of the building and the climatic conditions, to say nothing of the materials - wood, slate, copper, or thatch that may be at hand. A steep gabled roof is suitable, for instance, when the building must shed snow all winter, or a flat roof when, as in Palestine, the house-dweller at the end of a day climbs up to the roof to get the cool air of evening.

1 Ibid:, pp. 13-22.

If stone gives one type of construction, mud gives another. Let us make big cubes of mud, dry them in the sun, and cement them together with wet mud to form a solid wall: this gives us the mud hut of the primitive Egyptian or the adobe house of New Mexico. Reduce the size of the cube, use clay, and bake it with fire in a kiln: it becomes a brick. The brick is a more flexible kind of stone, and, in the lowlands, where wood and stone are sometimes hard to find in the marshes or the grassy plains, and clay is plentiful, as in the neighborhood of Amsterdam or London, bricks will be the chief building material. If the clay is molded in a special form, hollow in the inside, and keyed so that it may be joined to another form, we call the stuff terra cotta: as such it is always used as a covering, for unlike brick it cannot stand up under a load.

There is still another important form of masonry. Make a wooden form to contain the foundations, the walls, and the horizontal supports of the structure, and pour into this form a mixture of cement and sand, reinforced with iron rods for greater strength. So built, the house becomes a single stone, bearing the shape of the original mold: the name of the construction is monolithic (single-stone) construction. The Romans knew the secret of this method and applied it in various ways, using bricks, for example, as the mold and concrete in the core. Their bridges, roads, amphitheaters are still standing. It has the strength and simplicity of stone; it has the flexibility of brick; it has a massiveness of its own; and, in addition, since concrete can be poured into a mold, it makes possible fresh external shapes, which may fit the inside of the building as the glove fits the hand. Ferro-concrete, finally, need not be confined to flat surfaces and right angles. Erich Mendelsohn, the German architect, has shown how it can be modeled in the mass, as the sculptor models clay.

Wood gives still another type of construction. It leads to frame construction; for, like steel, a relatively light piece of wood will carry a heavy load when placed on end. Bind the frame together, form a box, fill the intervening space with bark, and you have the Long House of the Iroquois Indian; cover it with bamboo and thatch, and you have the simple Japanese dwelling; make the timber a little more solid, to stand up against heavy storms, and fill in the walls with clay or mud-and-twigs, or with flint, or with brick, and you have the half-timber house of medieval France, England, and Germany. Cover over a similar form with clapboards, and you have one of the early forms of the American house.

The habit of building frame houses in America made the transition to steel, for the framing of tall buildings, fairly easy, except for architects who had been too thoroughly trained in the forms of pure masonry. In stone construction, each stone bears directly the load above it: take away a course of stones in the middle of the wall and the building topples. In frame construction, on the other hand, the load is distributed: no single part of the frame is essential, for the whole is knitted together: the wall ceases to be a support and becomes a curtain, and whereas a stone building could not possibly be lifted off its base and transported, it would be as easy to do this with a skyscraper as with a cottage, if we could have engines and rollers built on the same scale. Structurally, the building is complete when the frame has been put together. All other construction is merely to keep off the wind and the weather and to divide the interior space into suitable rooms.

Steel is an excellent material when height or a wide span is demanded. Its chief defects are that it rusts and conducts heat too easily; so it must be painted repeatedly to guard against the first danger, and, to prevent warping and buckling in a fire, it must be surrounded by a fire-proof, non-conducting material.

The dominance of steel in American urban architecture today is an exhibition of the way in which a technical achievement, the cheap manufacture of iron and structural steel, has worked hand in hand with a peculiar social situation - the concentration of a large part of the urban population in skyscrapers, for the sake of the rise in ground rents. Steel was in fact forced upon the architect by the business man. As a result, all but a handful of our high buildings bear the prime marks of their origin: they are rent-barracks, in which every detail is subordinated to the principal purpose of utilizing each last square foot of land, each possible cubic foot of enclosed air. Our skyscrapers are often as massive and powerful as a mountain; they are often, also, as unformed and as crude as a slag-heap.

These are the essential materials and forms. They are, for architecture, what words and letters are for language. Without them, there is no architecture. What use we put them to, however, depends upon the human purpose that the building must serve, the state of the arts, the taste and training of the builder, and all sorts of local matters like the site itself, the amount of sunlight available, the climate, and the very character of the earth in which the foundations must be sunk. Architecture is both the most human and the most earth-bound of the arts; and it reflects natural conditions and human characteristics in every phase of its development.

Now, each of these basic materials lends itself to a peculiar heightening of its effects, so as to give greater "health, power, and pleasure" to the beholder.

Consider the stone mason. The quarry man, who merely shapes the rough stone into a block has his mind filled, perhaps, with the legends of the church and the memories of the countryside in which he grew up. There comes a time when he is no longer content merely to hew the stone; he wants also to shape it and to leave on it the imprint of his imagination: with that he becomes a sculptor. In the medieval cathedrals, so easy was it for the stone mason to pass into sculpture that scarcely a single surface remains untouched by the sculptor's art: satires, histories, legends, chapters of the Bible - all these crystallized in the stones of the cathedral, to make it a more complete expression of what the medieval man valued and loved.

Henry Adams has described this process in great detail in his magnificent book on Mont Saint Michel and Chartres. The same taste and skill, however, were applied to the most modest burgher's house. What keeps modern work done "in Gothic" from being alive is the fact that the skill and education and religion, which made it possible for numerous men to work on a common design, without having every detail marked down in the draughting office, no longer exists; one could scarcely trust a Catholic, a Baptist, and an Atheist to work their several wills upon a single church, without a little guidance. The mason's art has become largely mechanical reproduction. If the architect wants fresh and significant sculpture, he must limit it to the work that may be done by a single artist. This is what Mr. Bertram Goodhue did in the building of the Nebraska State Capitol; it accounts for the relative success of its sculptural decoration.

Wood differs from stone in its decorative capacities. Wooden beams and posts must not be carved too freely, or they will lose strength, and wooden sheathing, like clapboards, can scarcely be carved at all. Trimming, turning in a lathe, staining, and painting are the chief decorative resources of wood. These forms are common to the wooden buildings of Japan, the Alpine hut, and the American wooden cottage. Concrete, on the other hand, is a material that tends to present large unbroken surfaces, and they must either create their own texture and color, or be covered over, as the Romans so often covered their concrete, with a veneer of marble. Finally, as an offset to these bare surfaces concrete may be encrusted, at appropriate spots, with tile or mosaic, or the wide wall surface may be painted or stuccoed.

Bricks, on the other hand, instead of having a pattern applied to them, can form patterns of their own. By using the end or the side of the brick (the header or the stretcher as the mason says) in various combinations we may bond the material together to form a particular pattern and texture; at times the pattern may be an elaborate geometrical design, accentuated by bricks of different colors. The use of overburnt bricks may take away from the flat uniformity of surface; by jutting out the bricks at intervals a similar effect may be produced. In Holland, England, and Northern Italy there is a vast array of brickwork structures, whose decorative interest comes largely from this delicate self-ornamentation; and a good deal of the charm of Georgian architecture in brick is due not so much to the stereotyped classic details as to the quality and color of the brick surfaces.

Finally, steel and glass present new resources. Steel can be bent and laced together, for in general, only by casting will it take any other than its structural shape. The earlier builders in the seventies, who used steel, sought to mold it decoratively, as they did the girders in the oldest section of the Metropolitan Museum in New York. But the best steel work, that of the Eads Bridge in St. Louis or the train hall of the Pennsylvania Station in New York, for instance, does not attempt to achieve any other effect from steel than that which follows from its structural interlacing. As for glass, it must usually be applied or encrusted: within that limitation its range is almost infinite; and as the Exhibition of Decorative Art in Paris in 1925 showed, its possibilities are far from being exhausted.