The arch of Constantine was dedicated by the senate in AD 315 in honour of Constantine's victory over Maxentius. However, it is is generally understood that the arch is actually much older and was originally dedicated to emperor Hadrian. Constantine simply replaced certain panels and parts of it in order to make it his own.
And below is perhaps the most controversial panel on the arch of Constantine. It appears to depict the Sun God, the very deity which was Constantine's father (Constantius Chlorus) worshipped and which is ascribed to Constantine prior to his conversion to Christianity.
However, this arch celebrates the triumph over Maxentius, a victory Constantine later credited to the 'God of the Christians'.