I cleaned this up the best I could. I'd never seen a mint mark like it before. I "believe" it to be a Roman mint mark, possibly the 4th officina. I believe it to be: Gratian AE3. D N GRATIA-NVS P F AVG, pearl-diademed, draped and cuirassed bust right SECVRITAS-REIPVBLICAE, Victory walking left holding wreath and palm branch Mintmark RQVARTA What say you?
My Gratian Gratian (367- 383 A.D.) Æ 21 O: D N GRATIA-NVS P F AVG, Pearl-diademed, draped and cuirassed bust right. R: VIRTVS ROMANORVM, Roma seated facing, head left, holding globe and spear,Θ and Φ at sides, anta in ex. theta and phi officina Antioch Mint 2.5g RIC 50b(2)
Yours has much better lettering! Mine is all but obliterated on the obverse and I can only make out SECVRITAS and a few letters of the mint mark on the reverse. Still a fun detective job
the mint mark RQVARTA means it is the fourth workshop from the Rome mint P = Prima (1) S = Secunda (2) T = Tertia (3) Q = Quarta (4)
Warren (CT Valentinian) has a good section on these halfway down this page: http://augustuscoins.com/ed/RomeOfficina/Officina.html Rule of thumb: If you have a question on a coin in RIC IX and have not read what Warren has to say on the matter, you are making a mistake.
Gratian, AD 367-383. AR Siliqua, 16mm, 2.2g, 12h; Trier mint, 367-378. Obv.: DN GRATIANVS P F AVG; Pearl diademed draped cuirassed bust right. Rev.: VRBS - ROMA; Roma seated left, holding Victory on globe and sceptre // TRPS•Reference: RIC IX 27f Trier.