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HISTORY OF ENGINEERING. Rook I.

SQUARED STONE.

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OPUS INCERTUM.

that kind of construction called opus incerta prevailed, which must not be confoundedwith the work we see at Preneste, Cora, and other ancient cities of Latium. Vitruvius confirms us, and severalruins still show that theopus incerta was composedof small polygonal stones,set in mortar, specimensof which may be seen in aruin behind the temple ofRomulus, in the temple ofVesta at Tivoli, of Fortuneat Preneste, and in manyother ruins scattered overthe Campagna; whilst thewalls of the ancient citiesof Latium are formed ofpolygonal stones 4 or 5 feetin diameter, laid togetherwithout any cement. Theopus incertum is the ex-ternal coating of the wall,being backed or filled in 1S *

with all sorts of material. (S qq Jig. 116.)

To the opus incertum succeeded the opusreticulatum, which was in ordinary use atthe time Vitruvius lived, and continued tillthe time of Caracalla . At the same timeburnt brick was introduced.

The opus reticulatum (Jig . 117.) has thestones formed like wedges, and put togetherto resemble the meshes of a net; the stonesfound in the country were used, whateverthey might be composed of, and as theangles or quoins of their buildings could notbe executed properly with them, they usedfor this purpose tiles, or brick, or stone of arectangular form like them. In the gar-dens of Sallust at Rome, the house of Mae-cenas , which afterwards served for the sub-structions of the baths of Titus, we see theopus reticulatum used promiscuously withbrick.

Brick was early used for construction,became general in the time of Augustus ,and continued in use till the fall of the Romanempire; it is as solid, and perhaps moredurable, than stone.

Thus the Romans used squared stone duringthe time of their kings and the republic;

OPUS RETICULATUM.