system
Given the following post, respond as if you're commenting on Reddit:
human
[Halo] When was modern humanity's first encounter with Forerunner technology?
gpt
Onyx was discovered in 2491, and considering that the Assembly tried to dissuade any colonization efforts due to the presence of forerunner ruins (which would prove to humanity that extra-terrestrials existed) it seems reasonable to assume that this was the first time such ruins were discovered.

However, considering that artifacts have been found on Reach and even Earth, its possible that ONI had made such a discovery long before then and kept it well-hidden.