AE Follis (28mm, 5.8gm) Struck 309-312 A.D. Ostia

Obv: IMP C MAXENTIVS P F AVG Laureate head right

Rev: AETERNITAS AVG N Castor and Pollux, each with a star above cap, naked but for chlamys hanging from shoulders, standing facing each other, each leaning on scepter with outer arm and holding bridled horse with inner arm, wolf and twins between them MOST in exergue

RIC VI 16