Jeremiah 38:6

The nobles had Jeremiah placed in a cistern of one of the royal princes, Malchijah, which was in the court of the guardhouse. Jeremiah had previously been confined in this court or stockade (Jeremiah 37:21), but now he was lowered into the cistern with ropes. The cistern had no water in it, but the bottom was very muddy, and Jeremiah sank into the mud. The nobles wanted him to die there of "natural causes," i.e., hunger-probably to alleviate their guilt (cf. Genesis 37:18-20; Genesis 37:24; Genesis 37:26-27).

"A typical cistern was dug out of limestone rock and consisted of a narrow neck perhaps three feet across and three or four feet in depth opening into a much longer bulbous cavity of varying depth. Water from catchment areas was directed to the opening." [Note: Thompson, p. 638.]