Representation of the Cross in the Palace, and of Daniel at the Public Fountains
On the other hand one might see the fountains in the midst of the market place graced with figures representing the good Shepherd, well known to those who study the sacred oracles, and that of Daniel also with the lions, forged in brass, and resplendent with plates of gold. Indeed, so large a measure of Divine love possessed the emperor's soul, that in the principal apartment of the imperial palace itself, on a vast tablet displayed in the center of its gold-covered paneled ceiling, he caused the symbol of our Saviour's Passion to be fixed, composed of a variety of precious stones richly inwrought with gold. This symbol he seemed to have intended to be as it were the safeguard of the empire itself.
Source: Life of Constantine (New Advent)