2The origin and invention of the different species of columns having been discussed, it is now necessary to say something on the subject of their ornaments, how they originated, and upon what principles and for what purposes they were invented. In all buildings the timber framed work, which has various names, crowns them. The timbers vary as much in their uses as in their names. Those are called bressummers (trabes) which are placed over columns, pilasters (parastatæ), and antæ. In the framing of floors, beams (tigna) and boards (axes) are used. If the span of a roof be large, a ridge piece (columen) is laid on the top of the king post (columna, whence is derived the word column), and a tye beam (transtrum) and struts (capreoli) will be necessary. If the roof be of moderate span, the ridge piece (columen), and rafters (cantherii), of sufficient projection at their feet to throw the water off the walls, will answer the purpose. On the rafters are laid purlines (templa), and again on these, to receive the tiles, are placed common rafters (asseres), which must be of sufficient length to cover the walls and protect them.
2Since the origin and invention of the orders of columns have been described above, I think it not out of place to speak in the same way about their ornaments, showing how these arose and from what original elements they were devised. The upper parts of all buildings contain timber work to which various terms are applied. And not only in its terminology but actually in its uses it exhibits variety. The main beams are those which are laid upon columns, pilasters, and antae; tie-beams and rafters are found in the framing. Under the roof, if the span is pretty large, are the crossbeams and struts; if it is of moderate extent, only the ridgepole, with the principal rafters extending to the outer edge of the eaves. Over the principal rafters are the purlines, and then above these and under the roof-tiles come the common rafters, extending so far that the walls are covered by their projection.