system
Given the following post, respond as if you're commenting on Reddit:
human
[Attack on Titan] If humans can't safely leave the walls without being eaten by titans then how were the walls first built?

Massive thick walls taller, thicker, and longer than any seen in human history IRL would probably take decades if not centuries to erect; it's not like some overnight public works project.
gpt
The answer is super spoilery.

>!Way back in the day, titans could be controlled by a special individual; this power was passed via bloodline (i.e. the royal family). They created a bunch of colossal titans and used their bodies as the core of the wall. The walls aren't primarily to protect against the "feral" titans; they're a safeguard against other human nations, who understandably want to exterminate people who posses the power to control, create, and/or transform into titans.!<