Today is the Fast of the Tenth of Tevet

 https://www.israelnationalnews.com/news/420116

On Asarah B’Tevet in the year 3336, Nevuchadnetzar, king of Babylonia, laid siege to Yerushalayim, marking the beginning of the events that led to the destruction of the First Temple, the exile of the People of Israel from their land and soon after, the last vestiges of self rule for those who remained. The story is recounted at the end of the Book of Kings, Chap. 25:

To commemorate the tragic day when the siege began, the Nevi’im (Prophets)[1] instituted the ta’anit tzibbur (communal fast day) of Asarah B’Tevet.

The Israeli Chief Rabbinate ruled that the Tenth of Tevet be considered Holocaust Martyr's Day, the general memorial day, Yom Hakadish Hakllali, for those who perished in the Holocaust but whose yahrzeit is unknown. Relatives may recite the kaddish prayer for them on this day and it is customary for the synagogue service to include the "El Malei Rachamim" prayer, said at funerals, on yahrzeits and on the days when Yizkor is said, in memory of all the victims.