The pantheon is even older than the Colosseum. It has massive Columns and you can see many holes in the top, much like the Colosseum. The holes are not due to erosion but were created during the Middle Ages. In the Middle Ages, metal became very short in supply and demand soared leading to the pilfering of many Roman buildings. Inbetween the blocks of the structure where small pieces of metal that helped to hold the structur together and this was what the villagers were after when they dug all these holes in to these magnificient buildings.