Constantinople was by far the most prolific and longest lasting of Byzantine mints.  The mint mark CONOB had become fixed on gold solidi as gold was only struck at Constantinople during the reigns of Anastasius I and Justin I; it appears on most subsequent Byzantine gold coins regardless of whether or not they were actually struck at the capital.  This was not the case with the subsidiary denomintions in bronze.  Variations of the mint mark include CON, CONOB, CONOS and COB.