The Twentieth of Sivan is a historic Jewish fast day, first instituted by Rabbeinu Tam in 1171. It originally commemorated that year's massacre at Blois in France, the first blood libel in continental Europe. [1]
The day was later also marked to commemorate the Cossack riots of 1648–49 in Poland-Lithuania, instituted by the Council of Four Lands in 1650. After World War II, suggestions were made to observe it as a Holocaust memorial day, but this was not widely adopted. [2] [1] [3] [4] In 1948, Tzvi Pesach Frank proposed to use the day to commemorate the fall of the Jewish Quarter in the Battle for Jerusalem. [5]