December 21 marks the winter solstice, "the darkest evening of the year" as the poet Robert Frost put it. It was known on Old English calendars as Geol, from which we get the English word "Yule".
December 21
Higgledy-Piggledy
Roman Divalia,
True winter solstice in
Terms of the sun,
Falls in the festival Saturnalicius
Day number five in a
Surfeit of fun.