Rock retaining walls pit friction against gravity

Q: Tim, I read a column on your website about rock retaining walls. I’m having a hard time believing you can build a lasting wall and not use mortar between the stones. I’d love to just build a wall and not have to use mortar. What’s the secret? – Karen, Bethesda, Md.
A: I routinely receive inquiries at my Ask Tim page at my website just like Karen’s question. You may be a person that marvels at retaining walls that hold back earth without using mortar or poured con