98 THE ATRIUM VESTZ. 
from the foundations. Their width, therefore, remains the same as in the 
preceding period. The wall on the north of the court also is at the west end 
8g centimeters wide, though further towards the east, a few courses above the 
foundation, it has been reduced to 60. The walls on the west are, with one 
exception, 60 centimeters, although those on the north are 75, as were the 
older ones. The walls in which are set the travertine bases for the columns 
are 89 centimeters. Bonding-courses, which are found only sporadically, 
if at all, in the earlier walls, appear regularly in those of this period. They 
are especially noticeable in the rooms on the southwest, where the tegule 
bipedales of which they are made are 4.50 to 5 centimeters thick and of a 
dark-red color. Since the walls on the north have been almost wholly rebuilt, 
only one bonding-course remains; upon the shelf’ formed by this rests the 
lower floor of the hypocausts. The courses of brick measure from 3.75 to 
4.25 centimeters, as in the last period, and the layers of mortar from 1.50 
to 2 centimeters. In the materials used, the type of construction differs from 
that of the time of Nero. The bricks are of the same type, many of them 
possibly left over from the earlier buildings. The mortar, however, is unlike 
that of the preceding period, showing a large proportion of red pozzolana. 
The concrete, especially that used in the foundations of the walls, is marked 
also by the large quantities of rare marbles which have been used as filling.’ 
1 This shelf, which is formed by the change in the width of the wall, at a little distance above the 
foundations, from 89 to 75 centimeters, is characteristic of this group of rooms. 
2 This is best seen in the foundations of the column wall on the west and of the wall opposite. 
