309 AD
Constantine believed he experienced a manifestation
of Apollo the sun God.

Apollo showed him victory in an up coming battle,
offered him wreaths and promised him thirty years
of rule.. Description of it has a sun like halo like we
see on cult image saints... He was victorious in battle
against Licinius and did rule for 30 yrs as prophecized.

312 AD,
again prior to battle its alleged Constantine had a vision,
this time a cross in the sky and words that he would be
victorious. Which he was against Maxentius at Milvian Bridge. Although he did not see a Jesus, this time he
attributed such to a christian God rather that pagan.

Constantine also claimed that Christian God instructed
him to mark the shields of his soldiers with the 'Chi Rho'
or XP symbol we often associate with christianity.

Yet one must ask why a christian God would want him
to use symbol long associated with Paganism.
(XP being distinctly marked on coinage from Ptolemy III
3 rd. Century BC.)

-Bulletproof and Waterproof don't mean Idiotproof.