塚 means 'hillock'

Thank archaeologists for demystifying the Jomon and Yayoi eras (c. 14,000 BCE–300 CE). By examining shell mounds—glorified trash heaps—these scholars have determined what ancient people ate, owned, and valued. Bones from a Tokyo shell mound revealed that Jomon cannibalism existed. Moreover, archaeologists have found a crucial Jomon food source (Castanopsis nuts), unearthed bronze Yayoi-era vessels and Yayoi-era defensive structures, and uncovered about 15,000 goggle-eyed figurines (c. 3000 BCE–400 CE). Many look pregnant, so people likely associated them with fertility, also possibly believing that one could transfer illnesses into them and out of humans.