Valentinian I, 364-375. soliditatemque redintegrentur. ('There shall be no excuse that the collected solidi, from whichever tax revenue, as we have already mandated, shall be melted into ingots of pure and solid gold.') (Cod. Theod. 12.6.12). The law was implemented to combat fraud by corrupt tax collectors, who had tricked the treasury by handing over underweight (i.e. clipped) and debased solidi. Metal analyses have shown that the fineness of the solidi, which had dropped to circa 95 % by 366, increased once again to 99.5 % after 367, indicating that the payment of taxes in debased solidi had been a real problem in previous years. With the new system, the treasury not only avoided being defrauded, it also guaranteed the fineness of the new solidi struck from the gold ingots by marking them as OB(bryzum).


The 'OB' in the reverse mintmark is an abbreviation of obryzum (from Greek ὄβρυζον), translating as 'pure gold'. It first appears on solidi from Treveri, Constantinopolis and Antiochia in 367, following new laws established in 366-367, which mandated the melting of tax revenues paid in solidi to ingots of pure gold: nulla debet esse causatio, quin solidi ex quocumque titulo congregati, sicut iam pridem praecepimus, in massam obryzae soliditatemque redintegrentur. ('There shall be no excuse that the collected solidi, from whichever tax revenue, as we have already mandated, shall be melted into ingots of pure and solid gold.') (Cod. Theod. 12.6.12). The law was implemented to combat fraud by corrupt tax collectors, who had tricked the treasury by handing over underweight (i.e. clipped) and debased solidi. Metal analyses have shown that the fineness of the solidi, which had dropped to circa 95 % by 366, increased once again to 99.5 % after 367, indicating that the payment of taxes in debased solidi had been a real problem in previous years. With the new system, the treasury not only avoided being defrauded, it also guaranteed the fineness of the new solidi struck from the gold ingots by marking them as OB(bryzum)