I WONDER - Who Invented Concrete?

The Romans were able to construct impressive buildings due to their invention of concrete, a mixture of volcanic ash, lime, and seawater. This strong material has allowed many Roman structures to remain in excellent condition. Without concrete, iconic buildings like the Pantheon and the Colosseum would not have been possible.

Name at least two famous buildings that the Romans constructed using concrete.

Why would the Romans not have been able to build their great structures without concrete?