Albert Barnes Commentary Jeremiah 38:6

"Then took they Jeremiah, and cast him into the dungeon of Malchijah the king`s son, that was in the court of the guard: and they let down Jeremiah with cords. And in the dungeon there was no water, but mire; and Jeremiah sank in the mire." — Jeremiah 38:6 (ASV)

The dungeon - The cistern. Every house in Jerusalem was supplied with a subterranean cistern, so well constructed that the city never suffered in a siege from want of water. So large were they that when dry they seem to have been used for prisons (Zechariah 9:11).

Hammelech - See (Jeremiah 36:26) note.

The prison - The guard. They threw Jeremiah into the nearest cistern, intending that he should die of starvation. Some have thought that (Psalms 69) was composed by Jeremiah when in this cistern.