The kommerkiarios (Greek: κομμερκιάριος) was a fiscal official of the Byzantine Empire charged with the collection of the imperial sales tax or kommerkion.
[2] According to the late 4th-century Notitia Dignitatum, there were three comites commerciorum under the control of the comes sacrarum largitionum: one for Oriens and Egypt, one for Illyricum, and one for Moesia, Scythia Minor and Pontus (i.e. the Danube frontier and the Black Sea).
[2][4] Gabriel Millet, a French Byzantinist, considered the early kommerkiarioi as merchants of the Byzantine emperor, but his views are deemed questionable.
[2] On the seals of the 9th to 11th centuries, the kommerkiarioi appear to be in control of larger territories, such as Cyprus or Chaldia, or operating in trade centers such as Cherson, Abydos, and Erythrai.
[2] They held court titles, such as protospatharios of the Chrysotriklinos or mandator, but could have specifically "commercial" positions such as metretes (Greek: μετρητής, "measurer").