The architecture of the civilised world can be best understood by considering the great buildings of each important nation separately. The features, ornaments, and even forms of ancient buildings differed just as the speech, or at any rate the literature, differed. Each nation wrote in a different language, though the books may have been devoted to the same aims; and precisely in the same way each nation built in a style of its own, even if the buildings may have been similar in the purposes they had to serve. The division of the subject into the architecture of Egypt, Greece, Rome, &c., is therefore the most natural one to follow. But certain broad groups, rising out of peculiarities of a physical nature, either in the buildings themselves or in the conditions under which they were erected, can hardly fail to be suggested by a general view of the subject. Such, for example, is the fourfold division to which the reader's attention will now be directed. All buildings, it will be found, can be classed under one or other of four great divisions, each distinguished by a distinct mode of building, and each also occupying a distinct place in history. The first series embraces the buildings of the Egyptians, the Persians, and the Greeks, and was brought to a pitch of the highest perfection in Greece during the age of Pericles. All the buildings erected in these countries during the many centuries which elapsed from the earliest Egyptian to the latest Greek works, however they may have differed in other respects, agree in this--that the openings, be they doors, or be they spaces between columns, were spanned by beams of wood or lintels of stone (Fig. 1). Hence this architecture is called architecture of the beam, or, in more formal language, trabeated architecture. This mode of covering spaces required that in buildings of solid masonry, where stone or marble lintels were employed, the supports should not be very far apart, and this circumstance led to the frequent use of rows of columns. The architecture of this period is accordingly sometimes called columnar, but it has no exclusive claim to the epithet; the column survived long after the exclusive use of the beam had been superseded, and the term columnar must accordingly be shared with buildings forming part of the succeeding series. [Illustration: FIG. 1.--OPENING SPANNED BY A LINTEL. ARCH OF THE GOLDSMITHS, ROME.]