Theoros

Theoroi (Ancient Greek: θεωροί or θεαροί) in Ancient Greece were sacred ambassadors, messengers sent out by the state which was about to organize a Panhellenic Game or Festival. Theoroi were received and hosted by Theorodokoi.

In ancient Greece theoroi meant something like "observers". They were envoys sent by city-states to consult oracles, to give offerings at famous shrines or attend festivals.

Theoria was a word for their duties. It came to mean any act of observing, and was used by Greek philosophers, generally, in the sense of "contemplation".

...
Wikipedia