The Secrets of Engineering and the Splendor of the Achaemenid Empire | How Persepolis Survived 2,500 Years

Security was paramount. Surrounding the terrace and extending up the mountain were defensive walls and towers, constructed mainly of sun-dried brick but reinforced with stone bases. Ancient historians such as Diodorus of Sicily described Persepolis as the richest city under the sun, guarded by triple walls, some rising to nearly 27 meters. Bronze-clad gates and colossal statues ensured that no visitor could forget they were entering a seat of world power.