What did the Roman Empire use the volcanic ash for that came
from the local volcanoes

To make concrete

Concrete is the most widely used construction material in the world. ... “A natural process in the caldera produces lime and forms concrete-like rocks by mixing it with ash – the same volcanic ash that Romans used.” That mixing creates rock that is compositionally similar to Roman concrete, but stronger.

Romans used volcanic ash and mixed it with lime to make this iconic material,” she explained. “A natural process in the caldera produces lime and forms concrete-like rocks by mixing it with ash – the same volcanic ash that Romans used."

what is this news

explanation:

these civilizations were located around fertile rivers, where they could produce an abundance of crops