The romans' ingenious use of was instrumental in the construction of the great cathedrals of europe 1,000 years later the arch and key stoning concrete entablatures columns

The answer is concrete.

The Romans' ingenious use of concrete was instrumental in the construction of the great cathedrals of Europe 1,000 years later. Vaulting of concrete completed the building of the great cathedrals and amphitheater of the Romans. It also made the Pantheon dome and the Palestrina’s Sanctuary of Fortuna Primigenia. 

a. theta waves. this is because the person is in a light sleep which means the brain waves would show these kind of waves.