The fast also commemorates the death of biblical Ezra the Scribe, traditionally on the 9th of Tevet, and (cf. b. Megillah 9a-b) the Septuagint translation of the Torah into Greek.
Previous PaleoJudaica posts on the Tenth of Tevet are here and here. For still more, see the Chabad article here and the one by Aish.com here.
The fast runs today from dawn to sundown. A safe and healthy one to all those observing.
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