Due to discovery, experimentation, and exploitation of vaulting, concrete, and arches by the time of the Romans, their architectural monuments had as impressive interiors as they had impressive exteriors.Traditional Persians, Egyptians, Greeks, and Etruscans architectural monuments had impressive exteriors but lacked impressive interiors. This is because all relied on building in a post-and-lintel system that rendered their interior limited in size since they were used to support heavy loads to shore up their exteriors.