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two nails are to be driven into every joist, so that no 
part of the edges may warp. I do not mention the 
chestnut, beech, or the farnus, because neither of them 
is durable. The floor being prepared, fern, if at hand. 
and if not, straw, is to be spread over it, so that the 
timber may not be injured by the lime. On this is 
placed a layer of stones, each of which is not to be less 
than will fill a man’s hand. 
These being spread, the 
pavement is laid thereon. If the rubbish be new, let 
three parts of it be mixed with one of lime; but if from 
old materials, the proportion is five parts to two of lime. 
It is then laid on, and brought to a solid consistence 
with wooden beaters and the repeated blows of a number 
of men, till its thickness is about three quarters of a 
foot. Over this is spread the upper layer, composed of 
three parts of potsherds to one of lime, of a thickness 
not less than six inches. Over the upper layer the pave- 
ment is laid to rule and level, whether composed of slabs 
or of tesseræ. When laid with their proper inclination, 
they are to be rubbed off, so that, if in slabs, there may 
be no rising edges of the ovals, triangles, squares, or 
hexagons, but that the union of the different joints may 
be perfectly smooth. 
If the pavement be composed of 
tesserae, the edges of them should be completely smoothed 
off, or the work cannot be said to be well finished. So. 
also, the Tiburtine tiles, peaked at the points, should be 
laid with care, that there may be neither holloys on 
them, nor ridges, but that they be flat, and rubbed to a 
regular surface. After the rubbing and polishing, marble 
dust is strewed over it, and over that a coat of lime and 
sand. Pavements are, however, more fit to be used in 
the open air, inasmuch as timbers expanding in à moist 
atmosphere, and contracting in a dry one, or sagging in 
the middle, cause defects in the pavement by their settle¬ 
ments. Moreover, frosts and ice soon ruin them. But 
as they are sometimes required, they must be made as 
follows. Over the first flooring boards, others crossing