The arch is awesome, but the coin seems unofficial

and the seller wants $500 for it.

Constantine II
A.D. 325- 326
AE Follis
18 mm 2.3g
CONSTANTINVS IVN NOB C; laureate head right.
VIRTV-S AVGG, campgate, six layers, four turrets, no star above, arched door decorated with dots.
In ex. TA crescent RL.
RIC VII Arles 295 var