 Later in 321 , Constantine instructed that Christians and non @-@ Christians should be united in observing the venerable day of the sun , or Sunday referring to the sun @-@ worship that Aurelian had established as an official cult . Furthermore , and long after his oft alleged conversion to Christianity , Constantine 's coinage continued to carry the symbols of the sun . Even after the pagan gods had disappeared from the coinage , Christian symbols appeared only as Constantine 's personal attributes : the chi rho between his hands or on his labarum , but never on the coin itself . Even when Constantine dedicated the new capital of Constantinople , which became the seat of Byzantine Christianity for a millennium , he did so wearing the Apollonian sun @-@ rayed Diadem ; no Christian symbols were present at this dedication . 
