The Enterprise visits the planet Mintaka III in this episode. Mintaka is also the name of the Westernmost star of the three stars that form Orion's belt in the Constellation Orion. It is a white-blue Super Giant star located approximately 900 light-years from Earth, and is over 20 times larger and 7,000 times brighter than our Sun.
The Mintakan tapestry that is given to Picard by Nuria and the villagers was seen on Captain Picard's chair in his quarters in many subsequent episodes of Star Trek: The Next Generation and in all of the "Next Generation" films except Star Trek Nemesis.
The episode's plot bears some similarities to some aspects of Erick Von Daaniken's premise concerning extraterrestrials visiting Earth in ancient times. In this case, Liko mistook the Enterprise's use of technology to beam Liko to Sickbay and heal his wounds as magic due to their technological frame of reference only being at a Bronze Age level, as well as Liko mistaking Picard's name for that of a god (or "Overseer" in the Mintakan culture) and the scientist Palmer as a servant of "the Picard".
The title is related to the phase Quis custodiet ipsos custodes, a Latin phrase from the Roman treatise Satires of Juvenal, written around AD 100, variously translated as "Who watches the watchmen", "Who watches the watchers", "Who will guard the guards", "Who shall watch the watchers themselves", or something similar. Another Juvenal expression provided the title of Star Trek: Bread and Circuses (1968).
The "who watches the watchers" quote is sometimes incorrectly attributed to Plato. Although one of his debates in The Republic has a similar theme, he never writes anything that could be translated into that line specifically.