battery atop the acropolis, further destabilizing the site. Site Location and layout The city of Ai-Khanoum was founded at the southwest corner of a plain in the region of Bactria, at the confluence of the Oxus (modern Amu Darya) and Kokcha rivers. The plain, which covered an area of around , was triangular, being bounded by the rivers on two sides and the mountains of the eastern Hindu Kush on the third. The loess soil of the plain was naturally suitable for agriculture; the proximity to the rivers allowed for the construction of irrigation canals; and the nearby highlands provided herders with large areas of summer pasturage. The area was also rich in minerals: mines on the upper Kokcha in Badakshan were the only sources of lapis lazuli in the world, as well as producing copper, iron, lead, and rubies. The city was downstream from the confluence of the Oxus and Qizilsu, a tributary whose valley provided access to the mineral-rich Western Pamirs and Chinese Turkestan, but also formed a natural corridor for any potential northern invaders. Ai-Khanoum therefore served as a strategically important bulwark, despite not controlling a major crossing of the Oxus or any other large trade route. Reflecting the city's strategic importance, its founders built Ai-Khanoum to a high defensive standard. To the south and west lay the Kokcha and Oxus, respectively – both riverbanks were steep cliffs more than high, which presented a challenge to any amphibious assault. Meanwhile, any eastward approach was protected by a natural acropolis, around in height, which stretched about north from the Kokcha. This plateau also included a small citadel at its southeast corner – protected by the -high cliffs on two sides, and a small moat on the third; this fort served as the defensive headquarters of Ai-Khanoum. These natural defences were reinforced by walls that completely enclosed Ai-Khanoum's city and acropolis. The northern ramparts, which were not assisted by any natural features, were built to be particularly strong: the -high and -thick walls were built out of solid mud bricks and protected by large towers and a steep ditch. The size of these ramparts allowed a few defending soldiers to nullify siege engines and engage an attacking force with minimal casualties; the large scale also reflects the low confidence of the Greek architects in the strength of mud-brick walls. The main gate of the city was set in the