system
Given the following post, respond as if you're commenting on Reddit:
human
[Half-Life] Did the Citadel 'arrive', or was it built in place?
gpt
It arrived. Causing several city blocks to vanish in the process.

No one is quite sure how it happened anymore.

Rumors say that it was dropped down from space in one price and landed causing the chasm around it.

However knowing what we know now of the combine's technology it was likely delievered via some huge dark energy portal which destroyed all the area around it.