What was the primary material used in building the Colosseum in Rome?

Here I go guessing againL

a)  concrete and stone

If I am not mistaken it is concrete and stone and they also added salt so the bricks could be preserved for a long period of time

Actually, I didn’t thought they had concrete back then in the B.C or early A.D. Volcanic Rock, yes Limestone was commonly used brick and malter. Brick and mouldter..forgive my spelling. But you know best. Thank you Alexis, your so welcome!! 😘💕

The primary material used to build the Colosseum in Rome was concrete and stone

Concrete and stones was used to build the Colessium in Rome.

The primary material used in building the Colosseum was travertine limestone, a type of stone quarried from Tibur (modern-day Tivoli) near Rome. It was used for the main pillars, walls, and structural elements. Additionally, tuff, a volcanic rock, was used for other columns and radial walls. Roman concrete, invented by the Romans, was also a key material, particularly for the vaulted arches and foundations.

That would be limestone, for thousands of years limestone was used for building.