Genius Publicius Populi Romani (Guardian spirit of the Roman people) first appears on Roman coins from the early Republic, either as a winged infant riding a goat, or a young man crowning Roma. Since the reign of Nero, the Genius was recognised as protector of the emperor, and during the late third and early fourth century AD, it became a very common reverse type.

Genius is customary portrayed as a youth, often standing near an altar or thymiaterion. He is usually shown holding scales; cornucopiae; or a patera, and sometimes wears a modius.

The genius reverse design was standardised during the third century, and referred to the state only. However, emphasis shifted back to the emperor in the fourth century, when the legend GENIO POPVLI ROMANI was replaced by GENIO AVGVSTI or GENIO CAESARIS.

The reverse above left, for instance, of a follis of Diocletian (AD 284 - 305), depicts a Genius standing to the left, wearing a modius and sacrificing over an altar, the legend reads GENIO POPVLI ROMANI. On the right we have a follis of Maximinus Daia (AD 309 - 313) displaying a Genius wearing a modius and holding a patera and cornucopia, GENIO CAESARIS.