The two key structural advances made by the Roman builders were the orders and particularly the barrel vault. Both of the structural strategies were used in the building of the Flauvian Amphitheater in 70-80CE. This amphitheater was a colossal building used by way of a theater center that held sporting events and other performances that could be viewed by the public. The complete exterior of the theater is covered in diverse kinds of orders used just to decorate the building. The bottom level featured barrel vaulting entrances that led to seating. I believe the Romans built on such large scale because they had to. It was such an enormous empire and they constructed up big cities of people there needed to be a large gathering area for entertainment. If there weren’t large assemblies, they would have not developed to what they were able to flourish as much as they did.