Constantine II  337 - 340  A.D.

Coin Description Constantine II , AE 18mm, Grade??, The coin is struck only slightly off-center causing a small part of the legend to be missing obverse as well as reverse. The bronze looking parts of the coin where covered by a rock hard white substance when removed there was little patina left underneath. RIC VII Rome 289, RBC 354e, VM 38.
Obverse The portrait is of Constantine II a laureate, draped and cuirassed bust facing left. The legend reads CONSTANTINVS IVN NOB C meaning: CONSTANTINVS (his name) IVN (junior/the younger to distinguish him from his father with the same name) NOB C (Nobilitas Caesar / Royal Heir to the throne). The legend is continuous also an indication of Constantine's position as Caesar.
Reverse

The reverse shows a campgate (watchtower) with two signal beacons and a star between them. The legend reads PROVIDENTIAE CAESS which translates as "The foresight of the Caesars". The second S in CAESS means that there are other legitimate heirs to the throne, in this case another two Licinius II and Crispus. For a bit more on Providentia see here.

Mint The exergue reads: R T which stand for the third officina (Tertia) of the Rome mint with a wreath between the two letters.
The Entire Story The entire story of this coin would read: Constantine the younger the royal heir to the throne. The foresight of the Caesars in combination with the campgate might show that extra defenses are being built for the future defense of the empire.