Thomas Aquinas Commentary Lamentations 2:8

"Jehovah hath purposed to destroy the wall of the daughter of Zion; He hath stretched out the line, he hath not withdrawn his hand from destroying; And he hath made the rampart and wall to lament; they languish together." — Lamentations 2:8 (ASV)

Here he touches on the destruction of the citadel of Zion.

1. He presents the divine deliberation: the Lord has purposed, as if He has decided meditatively, without acting immediately; of the daughter of Zion, her citadel or Jerusalem herself. This is the counsel, that I have purposed upon all the earth (Isaiah 14:26).
2. He presents the just judgment: He has stretched out His line, as if to measure His justice, so that the punishment would equal the fault; He has not withdrawn His hand, for He has lessened nothing of the just punishment. A line shall be stretched out upon it, to bring it to nothing (Isaiah 34:11).
3. He shows the effect of justice: and the bulwark has mourned, that is, the ruins provoked mourning, as seen above: the ways of Zion mourn (Lamentations 1:4). The earth mourned, and faded away, and is weakened: the world faded away (Isaiah 24:4).