Physical Structure of the Site of Rome. 13 



its ancient name in that of Pietre Rouse. Livy states, that in 

 the early ages of Rome, some of the streets of the city were 

 paved with this kind of stone. Afterwards the more compact 

 and durable lava found in the neighbourhood, near the spot 

 where the tomb of Caecilia Metella stands, appears to have been 

 substituted for the softer tufa. They called it silex *. 



The granular tiifa is of a blackish or deep violet colour ; 

 light, friable, composed of grains of scoria? and ashes slightly co- 

 hering, and mixed with many fragments of simple volcanic mi- 

 nerals ; and it also often contains rolled pebbles of lava. It is 

 of far more frequent occurrence in the hills of Rome than the 

 stony tufa; it constitutes the chief part of the Pincian, Quirinal, 

 Viminal, Esquiline, and Palatine hills ; and it is found in great 

 abundance in the neighbourhood. It is found on the summit 

 of Monte Mario, and near Mons Sacer. In the former place, 

 it forms extensive and distinct beds, traversed by those natural 

 rents which so often occur in the stony tufa. In several places 

 it contains impressions of leaves of land vegetables. In some 

 situations it lies under the stony tufa, but in most cases it lies 

 over it. 



It is in this granular tufa that the numerous catacombs found 

 in and around Rome are almost exclusively excavated. These 

 subterraneous places were called Arenariae *!-, — a name still pre- 

 served in the appellation given to those pits from which they dig 

 pozzolano, for mixing with lime in making mortar, at Frosinone 

 (Frusino), and Signi (Signia). Vitruvius, speaking of the sand 

 used for making mortar, describes four kinds, — a black, a grey, 

 a red, and one which he calls carbunculus, the latter found in 

 Etruria. It appears by his description to be very similar to 

 that found at Viterbo, and in the Tusculan and Alban hills. 



• " Eodera anno (457, A. U. C.) sediles curules aliquot foenoratoribas diem 

 dixerunt ; quorum bonis multatls, ex eo, quod in publicum redactum est, 

 senea in Capitolio limina, et trium mensarum argentea vasa in cella Jovis 

 Jovemque in culraine cum quadrigis, et ad Ficum Ruminalem simulacra 

 infantium conditorum Urbis sub uberibus lupce posuerunt ; semitamque saxo 

 QUADRA TO a Capcna porta ad Mart is straventnt.^^ — Liv. x. 23. 



" Censores (578, A. U. C.) vias sternendas silice in urbe, glarea extra ur- 

 bem, substruendas marginandasque primi omnium locaverunt."— Liu. xli. 27. 



•f* " Asinius autem brevi illo tempore, quasi in hortulos iret, in Arenarias 

 quasdam extra portam Esquilinam perductus occiditur." — Cic. pr. ClvenL 13. 



