The Mesopotamians believed that the gods offered mankind omens, signs foretelling possible future events. Scattered throughout the omen series Shumma alu ina mele shakin ("If a city is set on a height"), one of the largest collections of unsolicited omens and their portended outcomes, are several that concern the fortification walls and main gate of a city.

[If a city]'s dump grows bishopweed, an enemy will surround that city's gate.
If an owl makes a nest in a hole in a city gate and fire spontaneously consumes the (temple) Bit Apsi—destruction of (the city of) Eridu.
If the parapet of a fortification-wall looks [like a monkey (but) you climb up the wall and] it is normal—destruction of (the city of) Nippur.
If the latch-hook of (all) the doors of the goddess's temple is...