The great head, arms and legs of the Colossus were carved from white marble, while the rest of the body consisted of a brick core and wooden framework, possibly covered with gilded bronze. Judging by the size of the remaining pieces, the seated, enthroned figure would have been about 12 meters (40 feet) high. The head is about 21⁄2 meters tall and each foot is over 2 meters long.

One of the two right hands of the Colossus. The statue's right hand is said by Eusebius to have held "a trophy of the Saviour's passion with the saving sign of the Cross", possibly therefore in the form of a staff with the sacred monogram XP affixed to it. Medals minted by Constantine at about this time show him so decorated. Eusebius further records the Latin inscription engraved below the statue, which may be translated as follows:

through this sign of salvation, which is the true symbol of goodness, i rescued your city and freed it from the tyrant's yoke, and through my act of liberation i restored the senate and people of rome to their ancient renown and splendour.

The great head is carved in a typical, abstract, Constantinian style ('hieratic emperor style') of late Roman portrait statues, whereas the other body parts are naturalistic, even down to callused toes and bulging forearm veins. The head was perhaps meant to convey the transcendence of the other-worldly nature of the Emperor over the human sphere, notable in its larger-than-life-size eyes which gaze toward eternity from a rigidly impersonal, frontal face. The treatment of the head shows a synthesis of individualistic portraiture: aquiline nose, deep jaw and prominent chin characteristic of all images of Constantine, with the trends of late Roman portraiture which focus on symbolism and abstraction, rather than detail.