How did the rebuilding of Troy create a mound with many archaeological layers?

The ancient city of Troy, located at the mound of Hisarlik, consists of multiple archaeological layers because of the way the site was repeatedly rebuilt over thousands of years.12

Whenever a settlement was destroyed—typically by fire, earthquake, or warfare—the survivors did not clear the wreckage down to the original ground level. Instead, they leveled the debris and used it as a foundation to construct new buildings directly on top of the ruins. This process of building, occupying, and destroying occurred over many centuries, resulting in a massive accumulation of debris that formed a mound rising 105 feet (32 meters) above the surrounding plain.2

Archaeologists have identified a sequence of 10 principal strata (labeled Troy 0 through IX) that represent these distinct periods of occupation, with the oldest settlements at the bottom and the most recent at the top.12