A small spring of water (probably the first cause of the sinking in the earth) had bubbled up into the space in the brick-work, which bit by bit, and year by year, it had gradually undermined.

Nor did it remain stagnant at this place.

It trickled merrily and quietly onward--a tiny rivulet, emancipated from one prison in the ground only to enter another in the wall, bounded by no grassy banks, brightened by no cheerful light, admired by no human eye, followed in its small course through the inner fissures in the brick by no living thing but a bloated toad, or a solitary lizard: yet wending as happily on its way through darkness and ruin, as its sisters who were basking in the sunlight of the meadows, or leaping in the fresh breezes of the open mountain side.
Raising his eyes from the little spring, Ulpius next directed his attention to the prospect above him.
Immediately over his head, the material of the interior of the wall presented a smooth, flat, hard surface, which seemed capable of resisting the most vigorous attempts at its destruction; but on looking round, he perceived at one side of him and further inwards, an appearance of dark, dimly-defined irregularity, which promised encouragingly for his intended efforts.

He descended into the chasm of the rivulet, crawled up on a heap of crumbling brick-work, and gained a hole above it, which he immediately began to widen, to admit of his passage through.

Inch by inch, he enlarged the rift, crept into it, and found himself on a fragment of the bow of one of the foundation arches, which, though partly destroyed, still supported itself, isolated from all connection with the part of the upper wall which it had once sustained, and which had gradually crumbled away into the cavities below.
He looked up.