The Greek theater was the first one which was built artificially and the Roman theater was erected as creative form following the Greek theater The style of these ancient theaters has influenced modern theater. In terms of the purpose and function of the theater, the Greek was derived from religious purpose but the Roman was derived for amusement. We can observe several differences in comparing the Greek with the Roman theater. In the shape of the theater, the Greek theater was dignified and grand and had an open-air structure, but the Roman theater was splendid and ornamental and had a roof over the stage. In the character of the theater, the Greek theater was democratic but the Roman theater was partial. The Greek and Roman theaters have became one source of the modern theater as the Greek and Roman plays have became the source of the modern play, although there are several differences according to the social and dramatic characters.