Example Illustrated: Parthenon in Athens, Greece
See the image with the precisely-spaced Doric columns supporting the entablature. Note the overall feel of proportion and symmetry.
Another example: the Colosseum in Rome, Italy
This architectural style is also known as Greco-Roman due to its usage in ancient Greece and Rome and was initially used in large religious stone temples of ancient Greece, then successively for other Greek, and later Roman, structures.
Principles of order, symmetry, geometry, proportion and perspective were very important and utilized in a proscribed fashion. These perspectives have been classified as “architectural orders” known as Doric, Ionic and Corinthian and the design requirements were strictly adhered to. The style is also known for use of rows of large columns topped with a base (entablature) to support a roof (colonnades); and the design of capitals atop columns is very recognizable and it one of the features distinguishing the three classic orders. Many structures have been built over the centuries imitating these classical traits.
Read more about Columns and Architectural Orders at Architectural Columns & Architectural Orders at Architectural Columns & Architectural Orders