[1] In the classical Greek world, theoroi meant something like "observers" and they were envoys sent by city-states to consult oracles, to give offerings at famous shrines or attend festivals.
Theoria was a word that referred to the duties of the theoroi; it came to mean any act of observing, and was used by Greek philosophers, generally, in the sense of "contemplation".
Once they entered a polis and were received by a designated host, also known as theorodokoi, they announced the exact date of the relevant Panhellenic Game, and declared what became known as an Olympic Truce.
[2] This declaration by the theoroi was essential because it ensured safe passage of spectators and competitors to the Panhellenic Game or Festival by mandating that all warfare that would interfere cease immediately.
These theoroi took part in many of the sacred rituals or sacrifices for the event, as well as, had their own personal honorary seats for observing the festival or game.
For example, a theoroi named Demosthenes from Olympia, sought to use his position as architheoros as a way of gaining an audience with Nikanor to discuss a decree that had been made.