Forgotten Fast Days: Zos Chukas HaTorah
On Motzai Shabbos Korach 5774, our dear, close family friend, Reb Chaim Daskal a”h, was niftar, after a prolonged and painful battle with cancer R”L. Never one to complain, Reb Chaim M’Yerushalayim (as he was commonly known) still exuded Simchas Hachaim and gratitude to Hashem even in his weakened and pain-filled state, the last time this author had the zechus to see him, merely a week and a half prior to his untimely passing. In fact, his tza’ava, will, reflected this as well, including how he wanted his own levaya, kevura, and shiva to be held.
One of the maspidim (eulogizers) at the levaya (at 1:45 A.M.!), Elimelech Lepon, mentioned that Reb Chaim passed away only after Shabbos was over, averring that the Malach HaMaves could not take have taken him on a Shabbos. You see, with an open house and a multitude of guests weekly, Shabbos was truly Reb Chaim’s special day. In fact, Mr. Lepon revealed that it was exclusively due to the merit of Reb Chaim’s extraordinary and warm Shabbos hospitality that won him over to personally begin keeping Shabbos properly.
When my father, renowned Kashrus expert Rabbi Manish Spitz, heard the tragic news of the passing of his Yedid Nefesh of almost 40 years, he enigmatically exclaimed ‘Zos Chukas HaTorah’! His intent was that the week of Parashas Chukas is ‘mesugal l’puraniyos’, a time that has seen much hardship and tragedy for our nation. Therefore, it was fitting that only after Shabbos of Parashas Korach had ended and the week of Parashas Chukas officially began, that such an incredible man, in the prime of his life, passed away.
Yet, there is no mention in the Gemara of the week of Parashas Chukas being one of tragedy, nor is it mentioned by the Rambam, Tur, or Shulchan Aruch! Not even in the Siman where tragedies and proper days to fast are mentioned, Orach Chaim 580! In fact, most are wholly unfamiliar with anything specifically attributed to this week. Yet, the Magen Avraham, citing the Sefer HaTanya (referring to Sefer Tanya Rabbasi; a far earlier source that the famous Kabbalistic work of the Shulchan Aruch Harav), tells of a terrible, albeit fascinating, historical tragedy.
Friday of Fire
The Magen Avraham prefaces his terrible tale by quoting certain writings explaining that it is “worthwhile for every Jew to cry for the burning of the Torah”. He then proceeds to tell of a customary annual fast specifically for this purpose, on Erev Shabbos Parashas Chukas. On that day, in the year 1242, twenty wagonloads (however the original versions state 24 wagonloads) filled with Gemaros and Talmudic literature (including many works of the Baalei Tosafos), were burned in Paris by agents of the Church and King Louis IX of France.
Talmud on Trial
The pretext to this mass burning was a public debate (later known as “The Disputation of Paris”) beginning in 1240 featuring Nicholas Donin, an apostate-Jew-turned-Franciscan-monk who petitioned Pope Gregory IX to prosecute the Talmud for 35 purported affronts to Christianity. The Pope ordered the banning and confiscation of all known manuscripts of the Talmud. King Louis IX, nicknamed “the monk king” due to his religious zeal, and later leader of the failed Seventh and Eighth Crusades, decided to put the Talmud ‘on trial,’ with Donin as the prosecutor.
Several of the most eminent rabbinical authorities in France were tasked to defend the Talmud: Rabbeinu Yechiel M’Paris, Rav Moshe M’Coucy (the SMa”G), Rav Shmuel M’Falaise, and Rav Yehuda M’Melun; the official verdict against them a foregone conclusion. King Louis gleefully executed the “judgment” by publicly burning the 24 wagonloads of confiscated Talmudic literature on this “Friday of Fire.”
The impact and importance of this loss was tremendous. Keep in mind that this occurred over 200 years before the printing press was invented, and each of these volumes was a priceless, handwritten manuscript. In fact, this was considered such an enormous loss for Klal Yisrael, that the famed Maharam M’Rothenburg, an eyewitness, composed an elegy for our loss, ‘Sha’ali Serufa Ba’Aish’, deemed so essential, that it is incorporated into the Kinos recited every Tisha B’Av (Kinah 41).
I Had a Dream…
The great rabbis at the time, at a loss to understand the extent of the tragedy, inquired of Heaven by means of a dream (known as a she’elas chalom) to discover whether this terrible event had been so decreed by Hashem. The heavenly reply was a succinct three words ‘Da Gezeiras Oraysa’. This is the Aramaic translation (see Targum Onkelus) of the opening verses to Parashas Chukas, “Zos Chukas HaTorah, These are the decrees of the Torah” (Bamidbar Ch. 19:2). The Rabbanim understood from this cryptic reply that the burning of the Talmud was indeed Heavenly decreed. Moreover, they gleaned that it was due to the proximity of the Parasha that the tragedy transpired, and not the day of the month.
Therefore, and as opposed to every other fast on the Jewish calendar, instead of a specific day established as a fast day, this one, designated a Taanis for Yechidim (fast for individuals), was set annually on the Erev Shabbos preceding Parashas Chukas. For those fasting, Asarah B’Teves would not be the only Taanis Tzibbur that practically occurs on a Friday.
Retribution for the Rambam?
Rav Hillel of Verona, a talmid of Rabbeinu Yonah, and another eyewitness to these events, wrote a famous letter in which he considered the burning of the Talmud as a clear sign of Divine anger and retribution for the burning of the works of the Rambam, in the exact same place in Paris not even forty days prior!
After the Rambam’s passing (in 1204), many great scholars who did not agree with his philosophical observations in his ‘Moreh Nevuchim’ and ‘Sefer HaMada’ banned his sefarim, with a tremendous controversy erupting throughout the Torah world. Eventually, a number of his detractors submitted copies of his work to the monks of the Dominican Order to determine whether the Rambam’s works contained heretical ideas.
The Dominican Friars, naturally, summarily concluded that the Rambam’s writings were not only false, but blasphemous. In 1234, in Montpelier, France, they publicly collected and burned all copies they found of ‘Moreh Nevuchim’ and ‘Sefer HaMada’. Similarly, in 1242, a fanatical mob burned many of the Rambam’s writings in Paris. Less than 40 days later, at the exact same site, the 24 wagonloads of the Talmud were burned, on Erev Shabbos Parashas Chukas.
According to Rav Hillel’s letter, the famed Rabbeinu Yonah, one of the Rambam’s primary opponents, took the Talmud burning as a Divine sign, and publicly and vociferously denounced his former position and opposition against the Rambam’s writings and instead emphatically concluded “Moshe Emes V’Toraso Emes, V’Kulanu Bada’in! - Moshe and his Torah are true (here referring to the Rambam), while we all are liars”. He planned on traveling to the Rambam’s grave (in Teverya) and begging forgiveness. Some say this tragic incident was the catalyst of Rabbeinu Yonah’s writing what came to be known as his Magnum Opus, ‘Shaarei Teshuva’.
Further Grounds for Fasting
After discussing the burning of the Talmud, the Magen Avraham offers another reason for fasting. On this very day, Erev Shabbos Chukas, two entire cities of Jews were brutally decimated, as part of the Gezeiras Ta”ch V’Ta”t, the Cossack massacres led by Bogdan Chmielnitsky ym”shin 1648-1649, as recorded by the Shach.
Although most know of the Shach as one of the preeminent halachic authorities due to his extensive and authoritative commentary and rulings on the Shulchan Aruch, yet, few know that he also wrote a sefer titled ‘Megillas Eifa’, detailing the horrific and barbaric slaughter of tens of thousands (he puts the total at over one hundred thousand!) of Jews, and hundreds of entire communities during these terrifying years. Among his entries he relates (in graphic detail) how two cities were totally wiped out on this same day in the year 1648 (5408). Hence, the Magen Avraham avers, that it is proper to fast (Taanis Yachid) on Erev Shabbos Chukas, due to both of these tragedies happening on this same day in history.
20th of Sivan
However, that was not the first of the tragedies of Gezeiras Ta”ch V’Ta”t. That occurred on the 20th of Sivan, 1648 (5408), when the Cossacks attacked Nemirov (Nemyriv), in the Ukraine, and destroyed the Jewish community, numbering over 6,000. Several hundred Jews were drowned; other burned alive. The shuls were ransacked and destroyed, with even the Torah parchments desecrated and used as shoes. Since this horrifying catastrophe was unfortunately the first of many to come in the following years, the Shach, at the conclusion of his ‘Megillas Eifa’, declared a personal fast on the 20th of Sivan for himself and his descendants.
This was soon codified as public fast by the Vaad Arba Ha’Aratzos, the halachic and legislative body of all Lithuanian and Polish Jewry. Indeed, the Magen Avraham concludes his passage that in many places in Poland, the custom is to fast on the 20th of Sivan for this reason. Additionally, the Shach, the Tosafos Yom Tov, and Rav Shabsi Sheftel Horowitz, as well as several other Rabbanim of the time, composed specific Selichos to be recited on this day annually.
The First Blood Libel and Massacre
However, the 20th of Sivan was not chosen as a fast day exclusively due to the annihilation of the hundreds of Jewish communities during Gezeiras Ta”ch V’Ta”t. It actually held the ignominious distinction as being the date of one of the very first blood libels, in Blois, France, almost 500 years prior, in 1171(4931)!
According to one of the Selichos recited on that day, ‘Emunei Shelumei Yisrael’, attributed to Hillel ben Yaakov, which lists the place and year of the tragedy, the King offered the 31 innocent Jewish prisoners (some listed by first name in the Selicha!), including several Gedolim and Baalei Tosafos, the chance to convert. When they refused, he ordered them burned alive! The martyrs recited Aleinu L’Shabayach in unison as the decree was being executed. Although, as detailed in the Selichah, as well asrecorded by an eyewitness to the atrocities, Rabbi Efraim of Bonn in his ‘Sefer HaZechira’, which was later appended to Rabbi Yosef Hakohen HaRofei of Avignon’s sixteenth century ‘Emek HaBacha’, a chronicle of the terrible devastation of the Crusades (starting in 1096/4856; known as Gezeiras Tatn”u), the martyrs’ bodies did not burn, still, this tragedy foreshadowed and portended future cataclysmic events for the Jewish people. In fact, this terrible libel was a major factor in the expulsion order of Jews from France a mere ten years later.
The great Rabbeinu Tam and the Rabbanim of the time instituted the 20th of Sivan as a fast day, even exclaiming that this fast is ‘akin to Yom Kippur!’ The Selichos established for 20 Sivan, aside for the one mentioned previously which actually describes the horrendous pyre in Blois, were authored by the Gedolim of the previous generations regarding the destruction of many Jewish communities during the Crusades (known as Gezeiras Tatn”u; many Kinos of Tisha B’Av are recited in commemoration of these tragedies as well), including Rav Shlomo HaBavli, Rabbeinu Gershom (Me’or Hagolah), and Rav Meir ben Rav Yitzchak, the author of Akdomus. Interestingly, several of the Selichos, especially the one titled “Elokim Al Dami L’Dami”, strongly reference and invoke the idea and essence of Korbanos in their theme; comparing the self-sacrifice of the Kedoshim of these decimated communities who gave up their lives Al Kiddush Hashem, to Korbanos offered in the Beis Hamikdash.
Re-Establishing the Fast
In fact, it is due to the dual tragedies that occurred on this day that the Shach declared the 20th of Sivan a fast day. In other words, he didn’t actually set a new fast day; rather, he re-established the 20th of Sivan as a fast day, as it already had the distinction of a day that went ‘down in infamy’ almost 500 years previously. Therefore, it was only fitting to commemorate the unspeakable Cossack atrocities with a fast, on this very same day, the day that the first Jewish community was destroyedas part ofGezeiras Ta”ch V’Ta”t.
Chronicles of the disastrous occurrences of this day do exist and can still be found. Aside for the Shach’s ‘Megillas Eifa’, there is also Rav Nosson Nota of Hanover’s ‘Yavein Metzulah’, Rav Avraham ben Rav Shmuel Ashkenazi’s ‘Tzar Bas Rabbim’, Rav Gavriel ben Yehoshua of Shusberg’s ‘Pesach Teshuva’, and Rav Meir ben Shmuel of Sheburshen’s ‘Tzok HaItim’, all written by eyewitnesses to the carnage and wanton destruction. 
Although nowadays it seems not widely commemorated or even known about, nevertheless, the 20th of Sivan is still observed among several Chassidic communities, mostly of Hungarian origin. During the Holocaust, Hungarian Jewry was R”L decimated mainly over the span of the months of Iyar, Sivan, and Tamuz in 1944. Therefore, Rabbanim of Hungary re-established the 20th of Sivan as a fast day for Hungarian Jewry.
Recent events have proven to us the timelessness of the dictum of ‘Zos Chukas HaTorah’ - where tragedies beyond our understanding happen to the Jewish people in exile. Our pain and tears over the years have driven home the point to us that throughout our long and protracted exile there have been no dearth of reasons to fast. May we soon welcome Moshiach, and have no further need for fast days.
The author wishes to thank Rav Yitzchak Breitowitz for his assistance in clarifying much of the historical content of this article.
This article is dedicated L’Ilui Nishmasam shel R’ Chaim Baruch Yehuda ben Dovid Tzvi and Naftali Frankel, Gilad Shaar, and Eyal Yifrach Hy”d.
This article was written l’zechus for Shira Yaffa bas Rochel Miriam v’chol yotzei chalatzeha for a yeshua sheleimah teikif u’miyad!
For any questions, comments or for the full Mareh Mekomos / sources, please email the author: email@example.com.
Rabbi Yehuda Spitz, author of M’Shulchan Yehuda on Inyanei Halacha, serves as the Sho’el U’Meishiv and Rosh Chaburah of the Ohr Lagolah Halacha Kollel at Yeshivas Ohr Somayach in Yerushalayim.
His recently published English halacha sefer, “Insights Into Halacha: Food: A Halachic Analysis,” focusing on the myriad halachos related to food, is now available in Jewish bookstores worldwide as well as through Feldheim.com.
A book review is available here: https://www.theyeshivaworld.com/news/headlines-breaking-stories/1951391/seforim-in-review-food-a-halachic-analysis.html
 Magen Avraham (O.C. 580, end 9), quoting the Sefer Tanya Rabbasi (end 58, Inyan Arba Tzomos pg. 63b). This version of the tragic events is also later cited by the Elya Rabba (ad loc. 4), Aruch Hashulchan (ad loc. 4), Mishna Berura (ad loc. 16), and Kaf Hachaim (ad loc. 31). The Tanya Rabbasi is an early halachic work written anonymously by a Rishon who was a colleague of the Shibolei Haleket and Maharam M’Rothenburg. Nowadays, it is generally attributed to Rav Yechiel ben Rav Yekusiel M’Mishpachas Ha’Anavim, of the Chachmei Rome (see the recent Mossad Rav Kook edition of the sefer). Interestingly, the Tanya Rabbasi was merely quoting the Shibolei Haleket’s account; ergo, it is unclear how slight variations crept into the Magen Avraham’s retelling.
 The Oz V’Hadar Mishna Berura (ad loc. 16) references this to be referring to the teachings of the Arizal (Shaar HaKavannos of Rav Chaim Vital, Drushei Tikkun Chatzos 1 and Pri Eitz Chaim, Shaar Tikkun Chatzos Ch. 3).
 Indeed, the Biurei Maharsha”h (on the Tanya Rabbasi ad loc. 8) points out that there must have been a ta’us sofer in the Magen Avraham’s writing, as in original he was quoting, it explicitly states 24 wagonloads and not 20.
 The full proceedings of this debate was recorded by one of the Rabbanim who defended the Talmud, Rabbeinu Yechiel ben Yosef, the Rosh Yeshiva in Paris and father-in-law of Rav Yitzchak M’Corbeil, author of the SMa”K, in a sefer titled ‘Vikuach Rabbeinu Yechiel M’Paris.’ For more background on this tragedy, see ArtScroll’s Kinos and Tefillos for Tisha B’Av (Introduction to Kinah 41).
 For his leading role in this pivotal event amid a lifetime of royally advancing the banner of Catholicism, Louis IX is the only French king to have been posthumously canonized as a “saint.” [Hence, there are many cities named after him around the world, including one with a famous “Gateway Arch” in Missouri.] The papal edict against the Talmud was overturned by Gregory IX’s more tolerant successor, Pope Innocent IV in 1247. Disapproval from his peers notwithstanding, Innocent IV wrote letters to King Louis IX effectively ordering that henceforth the Talmud should be censored rather than burned.
 See Shu”t Menachem Meishiv (vol. 2, pg. 262, 62; part of the sefer Tziyon L’Menachem) who cites that approximately 12,000 individual volumes were burned!
 Aside for the Kinah he wrote, the Maharam referenced this great loss in his responsa (Teshuvos Maharam M’Rothenburg 250), citing the reaction of Rav Shmuel M’Falaise, one of the Rabbanim who unsuccessfully attempted to defend the Talmud from being burned. On a historical sidenote, the Maharam M’Rothenburg was niftar in captivity after being unjustly imprisoned for seven years in Ensisheim Fortress, in order to force the resident Jews to pay an exorbitant ransom to fill the king’s (Rudolf I of Germany) depleted coffers. The Maharam refused to allow himself to be ransomed, fearing that it would set a dangerous precedent of rulers holding Rabbanim captive and forcing the unfortunate Jews to pay the price. Indeed, a short while after his passing, the king attempted to do the same for the Maharam’s prized pupil, the Rosh, who only narrowly avoided capture, escaping to Spain. Tragically, the Maharam’s body was only allowed to be buried fourteen years later, when a ransom was paid by Alexander ben Shlomo Wimpfen, who was subsequently laid to rest beside the Maharam, in the Jewish cemetery of Worms, Germany (also known as “Heiliger Sand”), nowadays commonly considered the oldest surviving Jewish cemetery in Europe.
 In an interesting side point, the Goren Dovid (Shu”t O.C. 41) utilizes this tragedy as a reason to explain why nowadays Yom Tov Sheini is still observed. Unfortunately, throughout our long and bitter Golus we never know when a government might make a gezeira ra’ah and all halachic literature lost. How then will we be able to properly calculate the months and years to know when are the correct days to observe? He explains that this was a fulfillment of the Gemara’s warning (Beitzah 4b) to keep Yom Tov Sheini “Hizharu B’Minhag Avoseichem B’Yadeichem”, “You should still be vigilant with the custom of your forefathers that has been handed down to you because there might be times when the local government will issue a decree and it will cause confusion”. For more on this topic see recent articles titled ‘Rosh Hashana: The Universal Two Day Yom Tov (and Why Yom Kippur is Not)’ and ‘One Day or Two? What is a Chutznik in Eretz Yisrael to Do’?
The Shibolei Haleket (263, Ha’arugah HaTishi’is Seder Taanis, Din Arba Tzomos; whom other sources are ostensibly based on) cites this as well, albeit with slight variations. First of all, from his writing it seems that he was also an eyewitness. Second, he refers to it as 24 (and not 20) wagonloads filled with ‘Sifrei Talmud, V’Halachos V’Hagados’, similar to the Maharam M’Rothenburg’s version. Third, according to his version, the heavenly response received was ‘V’Da Gezeiras Oraysa’, ‘And these are the decrees of the Torah’. Accordingly, the Rabbanim understood the response to mean that Yom Vav (the sixth day) of Parashas Chukas specifically was the gezeira. This ‘vav’ is understandably not present in our Targum Onkelos on the pasuk of ‘Zos Chukas HaTorah’, as the pasuk does not state ‘V’Zos’. As mentioned previously, this account is also the version in the original Tanya Rabbasi, as he was citing the Shibolei Haleket. Other variations include the Sefer HaTadir (32, Hilchos Taaniyos pg. 233-234) who cites that 24 wagonloads were burned like the other Rishonim, but writes that the Heavenly response was ‘Da Gezeiras Oraysa’ (without the ‘vav’) similar to the Magen Avraham’s version, and the Korei HaDoros (pg. 23a-b s.v. ukafi) who writes that 21 wagonloads were burned, but places the date of the Talmud burning 62 years later, right before the Jews were actually expelled from France. Interestingly, the Maharam M’Rothenburg makes no mention of the she’eilaschalom in his Kinah dedicated to this tragedy. Neither does the Mishna Berura (ibid.), who summarized the reasons for the fast. However, in a different vein, in his recently published manuscript, Rav Chaim Paltiel, a Rishon and talmid chaver of the Maharam M’Rothenburg writes (Perushei HaTorah L’Rabi Chaim Paltiel, Introduction to Parashas Chukas, pg. 527; thanks are due to Rabbi Avrohom Goldstone of England for pointing out this source) that the minhag in France was to fast annually on the 6th of Tammuz, as that was the date that the Talmud was burned. And a siman for this is ‘Zos Chukas HaTorah,’ which the Targum is ‘Da Gezeirasa D’Oraysa,’ meaning that on that date there was a gezeira on/against the Torah. It seems that both the Maharam, as well as Rav Paltiel were unaware of the she’eilaschalom, and Rav Paltiel understood that the fast to commemorate this tragedy was set as an actual date and not on the Erev Shabbos preceding Parashas Chukas. Since his manuscript was only first published some 30-odd years ago (5741), it is understandable why none of the Acharonim quoted his version of the events. For more on the topic of She’eilosChalomos in general, see Rabbi Eliezer Brodt’s Lekutei Eliezer (pg. 59-63) and Rabbi Mordechai Zev Trenk’s recent Magic, Mysteries, and Mysticism: Illuminating Insights on Esoteric Torah Topics (pg. 76–78 and 235–239).
 For more on this topic and why Asarah B’Teves is the only Taanis Tzibbur that can fall out on a Friday, as well as the halachos of a Friday fast, see article titled ‘Fasting on Friday? – Asarah B’Teves: Not Your Ordinary Fast Day.’.
 This letter is brought in Chemdah Genuzah (pg. 18), as well as Otzar HaGedolim (vol. 7, pg. 105), and cited in Torah L’Daas (vol. 2, Parashas Chukas pg. 280-281) and Kuntress Peninei Gevuros Akiva (Parashas Chukas pg. 3). Perhaps somewhat apocryphal, but certainly evocative, Rav Hillel mentions that the ashes of the burnt sefarim of the Rambam mixed together with the ashes of the burnt Talmud.
 These letters, back and forth between the great scholars of the time, have been collected as the third volume of Kovetz Teshuvos HaRambam V’Igrosav, titled ‘Igros HaKina’os.’
 For more on the historical aspects of this see Rabbi Avraham Meir Weiss’s recent Mishnas Chachamim (pg. 265, footnote 50) and the ArtScroll Kinos and Tefillos for Tisha B’Av (Introduction to Kinah 41).
 This is a paraphrase of the quote Chazal attribute to Korach after he was swallowed up by the earth at the conclusion of his ill-fated rebellion against Moshe Rabbeinu! See Gemara Bava Basra (74a), Midrash Rabba (Parashas Korach Ch. 18, end 20), Midrash Tanchuma (Parashas Korach 11), and Kli Yakar (Parashas Korach Ch. 16, 34 s.v. nasu).
 A genocidal and bloodthirsty mass murderer who could have given Adolf Hitler ym”sh a run as most notorious Anti-Semite in history, Chmielnitsky ym”sh is nevertheless still considered a national hero in Ukraine for being the father of Ukrainian nationalistic aspirations. The Cossacks’ sheer brutality and scale of their atrocities was unsurpassed until the Nazis. According to noted historian Rabbi Berel Wein, the only reason why the Cossacks did not manage to kill as many Jews as did the Nazisym”sh, was that there were no mechanized weapons to enable easy mass murder back in the 1600s. It was not due to lack of trying, R”l.
 Although this author could not find this sefer among the works of the Shach, I was able to locate it annexed to the back of Rav Shlomo Ibn Varga’s Shevet Yehuda, a fascinating (and unfortunately horrifying) work detailing the trials and tribulations Klal Yisrael has gone through in different lands over the millennia of our prolonged exile. Although Rav Varga died over a hundred years prior to Gezeiras Ta”ch V’Ta”t, the Shach’s shocking account and vivid descriptions of the massacres were later included in this important work. Essential reading on Tisha B’Av!
 The Shach added an additional reason why he chose this date (also cited in Shaarei Teshuva - O.C. 580, end 9): 20 Sivan cannot fall out on a Shabbos in our calendar, ensuring and enabling fasters to be able to do so on that day every year. The Shach (as well as later the Yaavetz in his Siddur Beis Yaakov and as mentioned in the special aleph-beis acrostic ‘Keil Malei Rachamim’ recited on that day for the Harugei Kehillos T”ach [V’Ta”t]; reprinted from an old manuscript that was printed in the Shach’s lifetime) especially mourned the loss of the city’s Chief Rabbi, Rav Yechiel Michel, a tremendous Talmid Chacham. Interestingly, a few short years earlier, the famed Tosafos Yom Tov, Rav Yom Tov Lipmann Heller, served as the town’s Rav.
 Pinkas Vaad Arba Ha’Aratzos; cited by the Taz (O.C. 566, 3; although he quotes it as the Vaad Shalosh Ha’Aratzos) and Shaarei Teshuva (O.C. 580, end 9), as well as Rav Nosson Nota of Hanover’s ‘Yavein Metzulah’, Rav Avraham ben Rav Shmuel Ashkenazi’s ‘Tzar Bas Rabbim’ (Reshumos vol. 3, pg. 279), and the Tosafos Yom Tov’s Hakdama to his ‘Selichos L’Kaf Sivan’. See also Yad Shaul (Y”D 228, end 136), Daas Torah (O.C. 580, 4), Siddur HaShlah, Siddur Bais Yaakov (of the Yaavetz), Siddur Derech Hachaim (of the Chavas Daas), Yesod VeShoresh HaAvodah (Shaar 9, Ch. 11) and the introduction to sefer ‘Yesh Manchilin’. This fast is also mentioned by several other authorities including the Magen Avraham (ibid. and in O.C. 568, 10), Elya Rabba (O.C. 566, 3), Maadanei Yom Tov (ad loc. 1; aside for the Selichos he wrote), Pri Megadim (ad loc. M.Z. 3), Eshel Avraham (Butchatch, O.C. 580; at length), Mishna Berura (ibid.), and Kaf Hachaim (ibid.).
 He was the son of the Shlah and Av Bais Din of Prague, as well as the author of Vavei Ha’Amudim. His Selicha was printed in the Siddur HaShlah. In the aftermath of these tragedies, the Tosafos Yom Tov (cited in the end of Shaarei Efraim, Hilchos Krias HaTorah) also composed a famous Tefillah against talking in Shul.
 The ignominious distinction of very first blood libel seems to have occurred in 1144, Norwich, England, after a boy, William of Norwich, was found dead with stab wounds in the woods. Although his death was unsolved, the local community of Norwich attributed the boy's death to the Jews. William was shortly thereafter acclaimed as a saint in Norwich, with ‘miracles’ attributed to him, with a cult established in his name. However, in this case, the local authorities did not convict the Jews due to lack of proof and of legal jurisdiction. Although this sordid affair marked the first official ‘Blood Libel’, on the other hand, Blois in 1171 was the first recorded time and place such baseless accusations were actually acted upon, concluding with a gruesome massacre of the town’s Jews, HY”D. Thanks are due to Stephen Posen for pointing out these details.
 For this reason alone, the Taz (O.C. 493, 2), although maintaining that one need only keep the restrictions of Sefirah only until Lag B’Omer, nonetheless, exhorts us to continue with the prohibition on weddings even after Lag B’Omer until shortly before Shavuos due to the horrific tragedies perpetuated by the Crusaders to many Ashkenazic communities during the second half of Sefirah (Gezeiras Tatn”u). See previous article titled ‘Switching Sefirahs? - Understanding Your Minhag and its Ramifications’.
 In fact, according to this source, the tragic events in Blois distressed Rabbeinu Tam so much that he passed away a mere 14 days later, 4 Tamuz 1171 (4931). However, Rav Shmuel Ashkenazi (Alpha Beta Tinyeisa D’Shmuel Zeira vol. 1, pg. 391) posits that this was not referring to the famous Rabbeinu Tam who was Rashi’s grandson, but rather his talmid, Rav Yaakov of Orleans who was called Rabbeinu Tam M’Orleans. He adds, citing that Oheiv Yisrael of Apta (end Parashas Mattos) that although not mentioning the terrible pyre on that day, related an astounding drush that the 20th of Sivan is the beginning of Yom Kippur. He adds a Biblical allusion to this from Parashas Ki Sisa (Shemos Ch. 17:16): “Ki Yad al Keis Kah” - Keis (Kaf-Samach) stands for Kaf (20) Sivan and Kah (Yud - Hei) stands for Yom Kippurim.
 Rav Shlomo HaBavli is referred to by the Rishonim with great veneration. For example, he is quoted by Rashi (Parashas Terumah Ch. 26:15 s.v. v’asisa) and the Rosh (Yoma Ch. 8, 19). The Maharshal (Shu”t Maharshal 29) writes that Rabbeinu Gershom, teacher of all Ashkenazic Jewry, learned Torah and received his mesorah from Rav Shlomo HaBavli.
 Shach, in the conclusion of his ‘Megillas Eifa’, also cited by the Shaarei Teshuva (O.C. 580, end 9) and Kaf Hachaim (ad loc. end 31). This double catastrophe on the same day as part of the cheshbon to renew the fast of the 20th of Sivan is also mentioned by the Tosafos Yom Tov in his Hakdama to his Selichos L’Kaf Sivan, and in Rav Meir ben Shmuel Sheburshen’s ‘Tzok HaItim’.
 Be forewarned: Much of the content is quite graphic and gruesome in its explicitness. The Cossacks’ sheer depravity, cruelty, brutality, and bloodlust, was simply unprecedented in scale and scope, R”L.
 Many of these works were collected and reprinted together around a hundred years ago in ‘Lekoros HaGezeiros al Yisrael’ (vol. 4). Additionally, there are several contemporary sefarim that give a summary of the tragedies of Gezeiras Tach V’Tat and the 20th of Sivan, including Sefer HaTodaah (vol. 2, Chodesh Sivan, Kaf B’Sivan, pg. 357-360), and Nitei Gavriel (on Hilchos Shavuos, Chelek HaBirurim 6, pg. 282-299). Especially of interest is Rabbi Yirmiyohu Kaganoff’s recent article titled ‘The Twentieth of Sivan’.
 There are several theories raised to explain this. See Yad Shaul (Y”D 228, end 136), and the Maharsham’s Daas Torah (O.C. 580, 4). One supposition is that the original decree from the Vaad Arba Ha’Aratzos to fast on the 20th of Sivan was only for a hundred years. Another theory is that the decree was only on Jewry who lived in those lands. In fact, the lashon of the Magen Avraham (O.C. 580, end 9), as well as the Mishna Berura (ad loc. 16), bears this out, as they only mention the fast as a ‘minhag Poland’. Moreover, the Tosafos Yom Tov himself, in his Hakdama to his Selichos L’Kaf Sivan, writes that the fast was encumbent upon all throughout the Arba Ha’Aratzos; implying that it was never accepted in other outlying lands. Nowadays, there are not many Jewish kehillos left in Poland or Ukraine to uphold this. Indeed, Rav Moshe Feinstein (Shu”t Igros Moshe, Y”D vol. 4, 57, 11 s.v. v’lo) and Rav Yitzchak Isaac Halevi Herzog (Shu”t Heichal Yitzchak O.C. 61, 3) [and although disagreeing in psak about the main inyan in their respective responsa] both wrote that the takana to fast on the 20th of Sivan was only observed in those lands.
 See Nitei Gavriel (ibid. pg. 297-299), citing the Pinkas Minhagim of Kehal Yereim of Budapest from 5706/1946 and the Mishnas Yaakov (O.C. 580). For example, the Belz minhag is to be very makpid with reciting the Selichos of the 20th of Sivan, including the later additions of special aleph-beis acrostic ‘Keil Malei Rachamim’ recited on that day for the Harugei Kehillos T”ach [V’Ta”t] (reprinted from an old manuscript that was printed in the Shach’s lifetime) as well as a more recent, albeit unfortunately similar,aleph-beis acrostic ‘Keil Malei Rachamim’ for the Kedoshei HaShoah (Ta”sh-Tash”h).
Disclaimer: This is not a comprehensive guide, rather a brief summary to raise awareness of the issues. In any real case one should ask a competent Halachic authority.
L'iluy Nishmas the Rosh HaYeshiva - Rav Chonoh Menachem Mendel ben R' Yechezkel Shraga, Rav Yaakov Yeshaya ben R' Boruch Yehuda, and l'zchus for Shira Yaffa bas Rochel Miriam and her children for a yeshua teikef u'miyad!