Greek and Roman architecture are together referred to as “Classical architecture,” as they share many characteristics including an adherence to the Classical Greek Orders of Architecture and a sense of symmetry and balance. But, there are some key differences. Whereas the Greeks favored marble, the Romans invented concrete, and they relied on this key building material in much of their architecture. Romans also emphasized circular forms and made extensive use of the arch, vault, and dome in their building projects, unlike the post-and-lintel structure of Greek buildings. While Greek buildings tended to feature cramped interiors built on a more human scale, Roman buildings had dramatically high ceilings and were generally more flamboyant than their Greek counterparts.