Constantine I AE3. 

Obv: CONSTAN-TINVS AVG, laureate head right 
Rev: PROVIDEN-TIAE AVGG, campgate, 2 turrets, 6 layers, star above, no doors. 
Mintmark: PLON

RIC VII London 293, rated C3

Courtesy of TimeLine Originals (www.time-lines.co.uk), March, 2011