Valens, AE3, 364-367 AD.

Obv: DN VLEN-S PF AVG (sic), pearl diademed, draped, cuirassed bust right
Rev: GLORIA RO-MANORVM, Emperor in military dress, advancing right, head left, holding labarum, dragging captive behind him.

Mintmark: R dot PRIMA

RIC IX Rome 15b, type ix(b) var (obv legend). Rare.
Engraver's error.

from a thread on Forvm Ancient Coins, April 2010.