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How did Babylon’s double walls and outer ramparts protect the city?

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Reconstructed Ishtar Gate at Babylon near Al-Hillah, Iraq, featuring blue walls decorated with rows of yellow and white animal reliefs and a central arched entrance. — Babylon A reconstruction of the Ishtar Gate at the ruins of Babylon, near modern Al-Ḥillah, Iraq.

Babylon’s defensive system was a sophisticated multi-layered structure designed to secure the city against external threats. The city was enclosed by a massive double wall, which was further reinforced by a fosse, or ditch, that provided an additional physical barrier on both sides of the Euphrates River.1

Beyond these inner defenses, the city featured an outer rampart of triple construction that stretched 11 miles (18 km) in length. This outer line met the Euphrates at the north and south ends of the city, effectively creating a protected zone that enclosed not only the urban center but also additional palace complexes and irrigated land containing a network of canals. The inner walls themselves were characterized as a towered and moated fortification system, which, combined with the city's eight fortified gates—such as the famous Ishtar Gate—provided a formidable deterrent against invasion.123