Fast of the Tenth of Teves 5763
 

Why do we fast on this day?
 

Answer(s):

The 10th of Teves is the first of four fast days commemorating the destruction of the Bais HaMikdash Rishon (the First Temple).  On this day, in the year 423 BCE (as reckoned according to the secular calendar) King Nebuchadnezzar of Babylon began a siege of Jerusalem which last three years, culminating with the destruction of the Temple.

Also (On the 8th of Teves): By order of King Ptolemy of Egypt (285 thru 246 BCE according to the secular calendar), Seventy Jewish Sages were "commissioned" to translate the Torah (The Chumash) into the Greek language.  This "translation/interpretation" was called the Septuagint, and, according to the Talmud, "three days of darkness descended upon the world." The fast day was instituted because it was then possible for an unlearned person to have access to the Written Torah, and to interpret/misinterpret it according to his own inclinations.

And (On the 9th of Teves): We commemorate the yartseits of both of the Sages Ezra and Nechemiah.  These Torah leaders had led the Jewish people in the rebuilding of the Temple.

When they were lost to us, they left a void that was all but impossible to fill.