96

HISTORY OF ENGINEERING.

Book I.

Tufa was much employed for reticulated work, which style of construction came into

use at the decline of the republic;time of Caracalla , it is supposedthat during or after that emperor’sreign it was discontinued. Thepepperino is a volcanic production,found at Albano, by which name it issometimes called; it is of a green-ish brown colour, and the resem-blance it bears to finely powderedpepper has given it the modernname. This stone, haying undergonethe action of intense heat, resists theaction of fire, equally with that stone v-called gabina. It was on that ac-count that Nero , after the great con-flagration in his reign, ordered thehouses to be faced with either one orother of these stones. Pepperino ismore solid than tufa, and resists theaction of the weather better; al-though to a certain degree it be-comes affected. The walls of Ser-vius at Rome are built with it, as may

and as there are few known examples of the

Fig. 111.

be seen in the remains near the Quirinal ; also the walls which enclose the forum of Nerva,and the cell of the temple of Antoninus and Faustina. The gabina is a volcanic pro-duction, found near Gabii, distant ten miles from Rome . In colour it resembles the pep-perino; it is harder, though of a more porous texture, and was much used for millstones.The travertine, or, as it was formerly called, tiburline, is found near Tivoli, on the banks ofthe Tiber; the ancient quarries remain, near the bridge of Lucano. This stone is calca-reous, formed from the mixture of some sulphureous water with thatof the Arno. It is veryporous, resists the action of the atmosphere, and becomes harder the longer it is exposed:it is easily calcined by fire. In the Coliseum, the sepulchre of Metella, and many monu-ments in the Via Appia , this stone has been used; at first drawing from the quarry it iswhite, but the air acting upon it soon gives it a yellow tint, which increases by time : from itshardness it was used for plinths and substructions, for isolated columns, ornaments, cornices,capitals, &c. We see it in the Tabularium , the temple of Fortuna Virilis, the arch of theGoldsmiths, &c. It was ordinarily quarried in large quadrangular masses, and the smallerchippings were used for filling in.

Vig. 112.

AHCH UK THE UOJ.tmin H*.