Constantine I AE Follis 4.35 gr, 22.90 mm. London. 312-313 AD.  

Obverse: CONSTANTINVS PF AVG, laureate and cuirassed bust right. 
Reverse: MARTI CO-NSERVATORI, Mars, standing right, helmeted and in 
military dress, holding reversed, upright spear, left hand on shield.

Star in left field
Mintmark PLN.  

RIC VI London 254; cf Sear 3863. Rare.
(Rare reverse legend break)

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