Vikings' fifth season had 20 episodes.
 The extra two seasons denoting the freezing and breaking up of the ice on rivers and lakes
 As mentioned above, Varro wrote that spring, summer, autumn, and winter start on the 23rd day of the sun's passage through Aquarius, Taurus, Leo, and Scorpio, respectively, and that (in the Julian Calendar) these days were February 7, May 9, August 11, and November 10

