Mattingly, H., E.A. Sydenham, C.H. Sutherland, R.A. Carson, The Roman Imperial Coinage 13 vols (London,  Spink, 1923-1994) VII, Aquileia (p. 404), 85.

2011.02 

Billon centenionalis of Constantine

2.58 g. c.AD 325

Obv.:   Laureate head of Constantine with the legend CONSTANTINUSAVG.

Rev.:    Legend DNCONSTANTINIMAXAVG, i.e "Of Our Lord (DN= Domini Nostri) Constantinus Maximus Augustus.

The reverse type is VOT. XX within two palm-branches surrounded by a laurel wreath. These "vows" (VOTA) were taken by either the emperor or representatives of the state to commemorate significant anniversaries of a reign, in this case the 20th. This would date the coin to c.AD 325, the period of these vows being reckoned in various ways (and sometimes the coins look either backwards to vows already taken or forward to those to come), but the coin type does anchor it more or less to that year.

At the base of the reverse we have AQP. This is the mint mark, identifying the coin as issued by the mint at Aquileia in northern Italy, and by the first (P=Prima) workshop or officina.

Mattingly, H., E.A. Sydenham, C.H. Sutherland, R.A. Carson, The Roman Imperial Coinage 13 vols (London,  Spink, 1923-1994) VII, Aquileia (p. 404), 85.