It is supposed to have been visible as early as the time of Aurelian, but is only particularly mentioned by Procopius, an historian of the sixth century, who relates that Belisarius, in strengthening the city against a siege of the Goths, attempted to repair this weak point in the wall, but was hindered in his intended labour by the devout populace, who declared that it was under the peculiar protection of St.Peter, and that it would be consequently impious to meddle with it.

The general submitted without remonstrance to the decision of the inhabitants, and found no cause afterwards to repent of his facility of compliance; for, to use the translated words of the writer above-mentioned, 'During the siege neither the enemy nor the Romans regarded this place.' It is to be supposed that so extraordinary an event as this, gave the wall that sacred character, which deterred subsequent rulers from attempting its repair; which permitted it to remain crooked and rent through the convulsions of the middle ages; and which still preserves it, to attest the veracity of historians, by appealing to the antiquarian curiosity of the traveller of modern times.
We now return to Ulpius.

It is a peculiarity observable in the characters of men living under the ascendancy of one ruling idea, that they intuitively distort whatever attracts their attention in the outer world, into a connection more or less intimate with the single object of their mental contemplation.

Since the time when he had been exiled from the Temple, the Pagan's faculties had, unconsciously to himself, acted solely in reference to the daring design which it was the business of his whole existence to entertain.

Influenced, therefore, by this obliquity of moral feeling, he had scarcely reflected on the discovery that he had just made at the base of the city wall, ere his mind instantly reverted to the ambitious meditations which had occupied it in the morning; and the next moment, the first dawning conception of a bold and perilous project began to absorb his restless thoughts.
He reflected on the peculiarities and position of the wall before him.
Although the widest and most important of the rents which he had observed in it, existed too near the rampart to be reached without the assistance of a ladder, there were others as low as the ground, which he knew, by the result of the trial he had already made, might be successfully and immensely widened by the most ordinary exertion and perseverance.