The comes was the successor of the Principate-era rationalis, and supervised those financial sectors that were left outside the purview of the praetorian prefects: the taxation of senators, the chrysargyron tax, customs duties, mines, mints and state-run mills and textile factories.
He also exercised some judicial functions related to taxation in his administrative courts in particular in matters of fiscal debt.
The office of the comes gradually declined in importance after the late 5th century, especially after Emperor Anastasius I (r. 491–518) abolished the hated chrysargyron.
He remained however one of the main fiscal ministers, controlling an array of bureaux (scrinia) and with an extensive staff detached to the provinces.
He was succeeded by the sakellarios and the logothetes tou genikou, who remained the chief fiscal ministers in the middle Byzantine period (7th–11th centuries).