Of the Statue of Constantine holding a Cross, and its Inscription
Moreover, by loud proclamation and monumental inscriptions he made known to all men the salutary symbol, setting up this great trophy of victory over his enemies in the midst of the imperial city, and expressly causing it to be engraven in indelible characters, that the salutary symbol was the safeguard of the Roman government and of the entire empire. Accordingly, he immediately ordered a lofty spear in the figure of a cross to be placed beneath the hand of a statue representing himself, in the most frequented part of Rome, and the following inscription to be engraved on it in the Latin language: by virtue of this salutary sign, which is the true test of valor, I have preserved and liberated your city from the yoke of tyranny. I have also set at liberty the roman senate and people, and restored them to their ancient distinction and splendor.
Source: Life of Constantine (New Advent)