Jinshanling Section, Great Wall, Hebei, China — Commissioned by the Ming general Qi Jiguang, this 10.5-kilometer section features 67 watchtowers and sophisticated defensive features including cannon ports and drainage channels. Qi Jiguang standardized watchtower design across the entire northern frontier during his tenure.
© Jakub Hałun, CC BY-SA 3.0, via Wikimedia Commons
