4 THE ATRIUM VEST. 
5. The character of the materials employed, as shown by the size, color, 
and composition of the bricks and by the color and composition o' 
the mortar. 
For the determination of the specific periods to which the various parts 
of the Atrium belong, a comparative study was made, especially with regard 
to the methods of construction and the materials employed, of all the build- 
ings in and near Rome to which a certain date can be assigned. To this 
evidence was added that afforded by the literature and coins. The number 
of brick-stamps accessible to me was not sufficient to warrant their use as 
evidence,’ except in a very limited sense. 
Periods in the Development of the Atrium: As a result of my investigation 
along the lines just indicated, certain important facts have been established 
and new conclusions reached concerning the architectural development of 
the Atrium. The structural units” of which it is composed, apart from those 
of the early republican building, the number of which it is impossible to 
determine accurately, are seven or, possibly, eight. These will be described 
more fully in connection with the discussion of the architectural details of 
the several Atria. ‘The stages in the history of the building represented 
by these seven units are, however, but five in number. While no conclusive 
evidence remains concerning the exact dates of these various stages, the 
periods to which they are to be assigned can, as will be seen, be definitely 
determined in all cases. 
The Imperial Atrium of the First Period: The building whose scanty 
remains lie a meter below the present level of the Atrium*® may be accepted, 
from its orientation and style of architecture, as the republican Atrium 
Vest. More than half a meter above this was erected another building, 
consisting of a court 45 meters long, which was surrounded on two or, 
possibly, three sides by a series of lofty rooms.* This later building, which 
differed in orientation and architecture not only from the earlier Atrium, 
upon the remains of which it was erected, but also from the other buildings 
of the precinct contemporaneous with it, belongs, as is evident from its 
construction, wholly to the imperial period. In the earlier of the two build- 
ings, the republican Atrium, whose architectural history extends from the 
early republican or even the regal period to that of the early Empire, many 
of the walls were restored more than once before their final destruction, and 
new walls were added, especially in the rooms which belonged at an earlier 
1The value of brick-stamps in determining the ? By a structural unit is here meant a building or a 
date of the structures in which they are found part of a building in which the construction 
has been greatly overestimated, owing to the is identical in type and the walls are con- 
failure to take into account the frequent use tinuous throughout. 
of new material in repairing old walls and Plan A, u-xu. 
of old material in constructing new ones, ‘Plan A and pp. 16ff, 

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