extravagant expenditure so as to cause ruin ; architectsthemselves, from the dread of punishment, would hemore careful in their calculations, and the proprietorwould complete his building for that sum, or a littlemore, which he could afford to expend. Those who canconveniently expend a given sum on any work, with thepleasing expectation of seeing it completed would cheer-fully add one-fourth more; but wdien they find them-selves burdened with the addition of half or even morethan half of the expense originally contemplated, losingtheir spirits, and sacrificing what has already been laidout, they incline to desist from its completion. Nor isthis an evil which occurs in buildings alone, but also inthe shows of gladiators in the Forum, and in the scenesof plays exhibited by the magistrates, in which neitherdelay nor hindrance is admitted, since there is a neces-sity for their being completed by a certain time. Thusthe seats for viewing the shows, the machinery fordrawing the Vela, and the contrivances for shiftingthe scenes, must all be prepared by a given day, thatthe people may not be disappointed. And in the pre-paration of all these much readiness and profoundthought must be exercised, because they cannot beexecuted without machinery, and the application ofvaried and extensive studies. Since, therefore, this isthe case, it does not seem foreign to our purpose,carefully and diligently to explain those principles onwhich a work should be formed previous to com-mencing it. But as neither the law nor custom com-pels the adoption of such a practice, and the prsetorsand sediles are bound every year to provide the ma-chinery for the sports, it appeared to me, O Emperor,highly expedient, as in the foregoing books I havetreated on buildings, to explain in this which closesthe treatise, the principles upon which such machinesare constructed.