<human>:  What are the major differences between Roman and Greek architecture?
<bot>: The major differences between Roman and Greek architecture include the use of columns, building materials, style of architecture, and decorative elements. Greek architecture was mainly based around columns, and the three primary orders of columns used were the Doric, Ionic, and Corinthian styles. Roman architecture usually did not use columns except in the monumental form, and instead used arches and vaults. The materials used by Greek architects were mainly stone, marble, and terracotta, whereas Roman architects used concrete, brick, tufa, and stone. Greek architecture focused on harmony and the perfection of geometry to create their structures, whereas Roman architecture was more utilitarian and practical in its approach. Finally, Greek architecture favored ornamental decorations such as gods and goddesses, whereas Roman architecture favored more abstract ornamentation.