Roman architectural innovations, ancient Rome, grandeur, columns, arches, domes, Pantheon, Colosseum, Roman Forum, monumental structures, ornate carvings, marble, limestone, travertine, rustic finish, grand scale, urban planning, sewage systems, aqueducts, roads, bridges, concrete, vaulted ceilings, clerestory windows, barrel vaults, groin vaults, ribbed vaults, pilasters, capitals, pediments, ornate facades, symmetrical compositions.