This feast day commemorates the massacre of the baby boys which King Herod ordered in Bethlehem, in an attempt to kill the infant Jesus Christ. The innocent babies were seen by the Catholic Church as the very first martyrs.
The 16th century Christmas carol, The Coventry Carol, which was sung on 28th December, referred to the massacre:
Herod the King, in his raging,
Charged he hath this day;
His men of might, in his own sight,
All children young, to slay.
Of course, the story of the massacre is told in the Gospel of Matthew. Herod asked the “Wise Men” to go and search for the Christ child and then to return to him: “bring me word again, that I may come and worship him also.” However, the Wise Men were warned in a dream not to return to Herod:
“Then Herod, when he saw that he was mocked of the wise men, was exceeding wroth, and sent forth, and slew all the children that were in Bethlehem, and in all the coasts thereof, from two years old and under, according to the time which he had diligently enquired of the wise men.
Then was fulfilled that which was spoken by Jeremy the prophet, saying,
In Rama was there a voice heard, lamentation, and weeping, and great mourning, Rachel weeping for her children, and would not be comforted, because they are not.” (Matthew 2: 16-18, Standard King James Version)