system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do they make perfectly geometric rock walls that are pieced together from seemingly random stones?
gpt
They put the flattest side forward. They fill in the odd-shaped gaps with mortar, and the larger gaps with small stones and mortar. Ultimately the top is still a bit jagged, so they usually top it with more mortar and some carefully hand-cut stones.