ROMAN ARCHITECTURE—BAGGALLAY. 655 
was done in trenches in the ground, within wooden molds, of which 
he found distinct marks on certain walls, or between two built faces, 
as described by Vitruvius in speaking of wrought stonework,’ one may 
very well admit the term concrete, even though the regularity of the 
larger stones suggests that they were laid in by hand rather than 
thrown in (pl. 3, fig. 1). But Vitruvius never by so much as a hint 
suggests the use of “ false work” in his time. He tells us, and the 
appearance of the walls at Pompeii, for instance, bears out the de- 
scription, that opus incertum consisted of rough quarry stones, “ one 
over the other bonded together ” *—in fact, a rubble wall, built, no 
doubt, with a larger quantity of mortar than we use, but built, not 
cast. Opus reticulatum he does not describe in detail, but evidently 
regards as a fashionable variety (which he does not altogether ap- 
prove) of incertum.’ As a matter of fact, it would not be possible to 
cast a wall faced with opus reticulatum, and would be very difficult 
even to build it behind boarding, especially the weather boarding, of 
which Middleton found traces. The facing was of small conical 
stones with square heads, which were required to fit neatly together 
on the face; to set them inside boarding a man must have worked 
overhand and without seeing what he was doing. Without the board- 
ing, however, there would be no more difficulty in building such a 
wall than in building a flint wall with split facing; and there can 
be little doubt that that is how it was done. It must, however, have 
been slow work. One- knows how necessary it is to go slow when 
building with flint or small rubble in lime mortar. After getting a 
foot or two one must wait for the mortar to set before putting more 
weight on, otherwise the work will bulge and twist. Now, mortar 
made with pozzolana, such as the Romans used, though it eventually 
gets extremely hard, does not in the first few days set appreciably 
faster than good lime mortar; and the Romans used it in large quan- 
tity. If one may venture to guess, it was this slowness that led after 
a time to the introduction of false work to support walls while in 
course of erection. It seems nearly certain it was unknown in the 
early years of the reign of Augustus, but it may have been intro- 
duced soon afterwards. The building activity of that reign was 
unprecedented, and would probably have demanded methods quicker 
than the old. On the other hand, most of the remains of the time 
are of squared stone or very neatly executed opus reticulatum, which 
can not have been built behind false work (pl. 2). Middleton’s 
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¢ The way in which a contrast is set up between the two, sufficiently excuses 
Doctor Middleton, as an amateur of building, for the mistake he makes in 
regarding incertum as applying, like reticulatum, to the facing of the wall 
only. There can be no doubt about the real meaning of the passage. 
