An immense, columned temple built almost entirely of marble, Athens's ancient Parthenon is the consummate example of classical Greek architecture. Its legendary balance was achieved through a number of devices employed to counteract certain peculiarities of human vision. Lines that appear straight in the Parthenon are found on measurement to be curved. Distances and widths that appear equal are in fact expertly varied. Columns taper and tilt inward, lending a certain lightness to the massive stone structure.