Question

What did the Roman Empire use

the volcanic ash for that came
from the local volcanoes

To make concrete

Answer 1

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."

Answer 2

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.