The mounds that are found in the Near East which are the result of prior cities built upon each other are called tells. Tells are only found in the the Near East during the Bronze Age when a certain type of defensive system was used. This defense was called a glacis and was common during that period of time. It consisted of digging a moat around the town and using the dirt to make a hill around the town or using it for the foundation of the town. it was the use of this system which allowed the layers of civilization to be built into the mounds we see today. When new offensive forms of warfare were used this defense no longer worked and the tells cease to exist after this time period.

(The Great Courses – The Holy land Revealed)