It is a long-established view that Roman coins were used as a means to convey messages. The obverse (“heads”) of Roman imperial coins always bore the image of the emperor, but the reverse (“tails”) was not standardized as modern coinage is today. Coin reverses commonly had the image of a deity, usually an abstract concept such as “Health”, “Courage”, but they might also advertise the completion of a major new construction project (the Colosseum, a new aqueduct), or desired behaviour, such as “fertility” (ie, have more children) or “loyalty of the army”. Coins were used by many Romans, but especially to pay the army, and for that reason coin reverses are a useful way to trace propaganda during civil and foreign conflicts. The 3rd century AD was a challenging period for the Romans, with almost continuous warfare and over 50 emperors and pretenders between 235 and 285. The frequent appearance of the god Sol (the Sun) on coin reverses in this period is a marked departure from the standard range of religious motifs and attests a major shift away from Jupiter. This thesis will investigate coins as an index of change by exploring where and how frequently the image of Sol was used on coins in the half-century prior to the establishment of a lavish temple to Sol in Rome around AD 273-275.