Roman architectural innovations, ancient Rome, grandeur, monumental, columns, arches, domes, Pantheon, Colosseum, Roman Forum, ornate carvings, intricate mosaics, rustic stones, travertine, marble, granite, vaulted ceilings, barrel vaults, groin vaults, ribbed vaults, clerestory windows, oculus, apse, basilica, triumphal arches, aqueducts, thermal baths, monumental gates.