Chap. XXIV.

MASONRY.

1421

In Volscinium, the capital of the Yolscii,are several remains : this style of masonry,found also at Tivoli, Pramcste, Terracina,l'ondi, Pompeii , &c., continued in useto the time of the emperors of Rome.It is generally formed of tufa, or smallstoues found in the neighbourhood of theconstructions; the angles, as well as otherportions of the wall, are carried up withtiles laid in regular courses; there are severalvarieties of opus retieulatum besides the twospecimens given.

Walls formed with triangular tiles arefound in the Coliseum and baths, &c.,of the imperial city ; other tiles of a squareor oblong shape pass through the entirethickness, at every third or fourth course,and the interior is filled with rubble. Inthe ruins of Pompeii are walls built oftufa, rough stone, and brick, executed in avery careless and inefficient manner; some-times only one course of brick alternateswith one of stone, at others three coursesof tile or brick intervene between oneof tufa or squared stone.

Whatever may be the character of the

-1_i

Fig. 2395. opus keticulatum with biuck.

/ n/\.

'W /x

v/\/\

Fig. 2396.

TRIANGULAR TILES.

masonry, one of the first considerationsis the arrangement of the footings, whichshould he constructed of stones as largeas can be obtained ; they should all besquared, brought to an equal thicknessin the same course, and laid upon theirnatural bed: the foundations shouldconsist of several courses, each decreasingill breadth as they rise, in proportion tothe thickness and height of the intendedwall; this decrease of breadth shouldtake place equally on both sides: ashlarfacing backed with brick or rubble workis often substituted for brick and tile ;but in those districts where stone is noteasily obtained, there can be no bettermethod than following the practice ofthe Romans.

In some ancient walls the bond-stonespass through the entire thickness, and

V _ \_

1

- I_L

Fig. 2397.

STONE AND TILES.

have a filling-in between the stretchers, composed of rubble or small stones bedded in mortar,the excellence of which has rendered them remarkably durable ; such walls are classedunder those called Pseudisodomon, from the courses varying in height.

Walls constructed partly of squared stone and rubble should have every second stone inthe same course to run entirely through the whole wall, so that the work may be preventedfrom splitting in the direction of its width ; the filling-in should be cautiously performed,and due regard paid to the shrinking of the mortar : the stone facing is sometimes rubbed