the wall to mark the place; and was about to retire, when he heard the
footstep of the sentinel on the rampart immediately above. Suddenly
cautious, though from what motive he would have been at that moment
hardly able to explain, he remained in the concealment of the trees and
bushes, until the guard had passed onward; then he cautiously emerged
from the place; and, retiring to some distance, fell into a train of
earnest and absorbing thought.

To account to the reader for the phenomenon which now engrossed the
Pagan's attention, it will be necessary to make a brief digression to
the history of the walls of Rome.

The circumference of the first fortifications of the city, built by
Romulus, was thirteen miles. The greater part, however, of this large
area was occupied by fields and gardens, which it was the object of the
founder of the empire to preserve for arable purposes, from the
incursions of the different enemies by whom he was threatened from
without. As Rome gradually increased in size, its walls were
progressively enlarged and altered by subsequent rulers. But it was
not until the reign of the Emperor Aurelian (A.D. 270), that any
extraordinary or important change was effected in the defences of the
city. That potentate commenced the erection of walls, twenty-one miles
in circumference, which were finally completed in the reign of Probus
(A.D. 276), were restored by Belisarius (A.D. 537), and are to be seen
in detached portions, in the fortifications of the modern city, to the
present day.

At the date of our story, then (A.D. 408), the walls remained precisely
as they had been constructed in the reigns of Aurelian and Probus.
They were for the most part made of brick; and in a few places,
probably, a sort of soft sandstone might have been added to the
pervading material. At several points in their circumference, and
particularly in the part behind the Pincian Hill, these walls were
built in arches, forming deep recesses, and occasionally disposed in
double rows. The method of building employed in their erection, was
generally that mentioned by Vitruvius, in whose time it originated, as
'opus reticulatum'.

The 'opus reticulatum' was composed of small bricks (or stones) set
together on their angles, instead of horizontally, and giving the
surface of a wall the appearance of a sort of solid network. This was
considered by some architects of antiquity a perishable mode of
construction; and Vitruvius a