Roman architecture was unlike anything that had come before. The Persians, Egyptians, Greeks and Etruscans all had monumental architecture. The grandeur of their buildings, though, was largely external. Buildings were designed to be impressive when viewed from outside because their architects all had to rely on building in a post-and-lintel system, which means that they used two upright posts, like columns, with a horizontal block, known as a lintel, laid flat across the top. A good example is this ancient Greek Temple in Paestum, Italy.

Since lintels are heavy, the interior spaces of buildings could only be limited in size. Much of the interior space had to be devoted to supporting heavy loads.