VOL. XXX.] PHILOSOPHICAL TRANSACTIONS. 275 



between 5 and 6 feet deep below the surface of the pavement, and full 23 inches 

 thick, which we may suppose to be 2 feet Roman measure. The bricks were 

 not in regular courses, as seen in those Roman buildings which are in view 

 above ground, but without order dispersed in the wall. The top of the wall 

 indeed was only 15 inches thick, and that was covered with the bricks which 

 bounded the pavement; but about 14 inches below the top there was a set off 

 on the inside of the wall 8 inches broad. We did not dig up the foundation of 

 the pavement to the bottom, but opened it at one corner only, that we might 

 discover how it was framed; for when it was bored through, they observed, 

 next under the tesserae, a bed of very strong mortar, more than a foot thick; 

 and under the mortar a bed of clay 2 feet thick, and under the clay a firm foun- 

 dation of brick. The clay, which the ground thereabouts does not afford, was 

 very fine, red, and close, doubtless having been carefully rammed. The surface 

 of the clay was neatly pitched with small flint and stones, pointed at their lower 

 ends, and headed at their upper ends. This pitching or paving is by Vitruvius 

 called statuminatio: and the stones it is done with, he calls statumina. 



This pitched work was exactly even with the set off in the inside of the wall: 

 on it was laid a bed of coarse mortar of about Q inches thick ; the skirts of this 

 mortar, which by Vitruvius is called rudus, rested on the set-ofF above-men- 

 tioned; it was composed of lime, with a sharp coarse sand, small pebbles, and 

 bits of brick. On this rudus was a finer composition, made, as near as I could 

 guess, with lime, a fine sharp sand, some kind of ashes_, and, which was the 

 greater part, stamped brick and pot-sherds, in grains not larger than cabbage- 

 seed, the flour or fine powder being separated from it. This bed was about half 

 a foot thick ; and is what Vitruvius calls the nucleus. Whether we may call it 

 terrace, I must leave it to those who are better skilled than myself, in giving 

 proper appellations to the several parts of masonry. Both this nucleus and the 

 rudus under it, nearly equalled the Portland-stone in hardness and compactness. 

 On this nucleus or terrace the tesserae were set on end; but with such exact- 

 ness, that two sorts of cement were used to fix them ; their lower ends standing 

 in a cement of lime only, well worked, and their upper halves cemented with a 

 fine grey mortar, consisting of fine sand, and as it seemed, ashes and lime. 

 This grey cement every where filled the intervals at their heads, and was much 

 harder than the tesserae themselves. 



The tesserae were only of two colours, white and a dark brown ; they were 

 harder than a glazed and well burnt tobacco-pipe, and of a somewhat finer grit; 

 the brown seemed to be of the same substance with the white, but coloured by 

 art, as Pliny informs us, the workers in clay of old had a method of doing, 

 they seemed to have been formed in a mould, and afterwards burnt. Hence I 



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