 However, the narrowing is not regular, but gently curved so that each columns appears to have a slight swelling, called "entasis" below the middle.The "entasis" is never sufficiently pronounced as to make the swelling wider than the base; it is controlled by a slight reduction in the rate of decrease of diameter.The Parthenon, the Temple to the Goddess Athena on the Acropolis in Athens, is referred to by many as the pinnacle of ancient Greek architecture.