Normally, in fact, those entrusted with kingship or any other rule confide least in the people closest to their predecessors; but Daniel enjoyed the same trust from all, receiving equal privileges and being entrusted with the same governance—hence, of course, his becoming one of the three supervisors under Darius. Now, by “supervisors” I think there is reference to what are now called viceroys, and by “satraps” to the governors of the nations, Daniel being one of the supervisors.
[AD 458] Theodoret of Cyrus on Daniel 6:2