1598

THEORY AND PRACTICE OF ENGINEERING.

Book II.

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The Arch of Sergius atPula is a perfect square,without attic, like that ofTitus.

The Arch of Titus atRome , raised by the senateand Roman people to com-memorate the conquest ofJudaea, is one of the bestexamples of proportion thatremain: built of whitemarble, it is a monumentof constructive art, someof the blocks being 9 feetsquare, and 2 feet thick; thearch is composed of elevenvoussoirs 16 feet deep.

For a detailed accountof its construction and or-nament the reader is re-ferred to the “ ArchitecturalAntiquities of Rome ”

The proportions are asquare, as is the openingof the archway, up to thespringing; and not a doublesquare, as described bySerlio . The pedestals arein height nearly half theopening of the archway,which Palladio observeswas the ordinary proportion Fig ' 2993 'given by the ancients. The entire length of the upper member of the cornice in thisexample is 48 feet, which dimension corresponds with the entire height, almost to a fraction:the width of the opening is 17 feet 6 inches, a trifle more than one-third of the entire width :bounding the facade by a parallelogram, excluding the attic, and drawing two diagonals,we obtain the centre from which the arch is struck, which rule will apply to the other

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AKCH OP SERGIUS AT POLA.

Fig. 2994.

ARCH OF TITUS AT ROME .