Isaiah 22:11

“Ye made also a ditch between the two walls, &c.] The outward and the inward; for Hezekiah not only repaired the broken wall, but he built another without, (<143205>2 Chronicles 32:5) and between these two he made a ditch, or receptacle for water; for rain water, as Kimchi says; that the inhabitants might not want water during the siege; but the end for which it was made follows: for the water of the old pool; which, being without the city, was by this means drained into this ditch or receptacle; and so the Assyrians were deprived of it, and the inhabitants of Jerusalem more abundantly supplied; this was wisely contrived to distress the enemy, and to enable themselves to hold out the siege…”

“Ye made . . . a ditch--rather, "Ye shall make a reservoir" for receiving the water. Hezekiah surrounded Siloah, from which the old (or king's, or upper) pool took its rise, with a wall joined to the wall of Zion on both sides; between these two walls he made a new pool, into which he directed the waters of the former, thus cutting off the foe from his supply of water also. The opening from which the upper pool received its water was nearer Zion than the other from which the lower pool took its rise, so that the water which flowed from the former could easily be shut in by a wall, whereas that which flowed from the latter could only be brought in by subterranean conduits (compare see on Isa…”

“Ye made also a ditch - That is, they made a “reservoir” to retain the water. The word ‘ditch,’ however, will well describe the character of the pool of Gihon on the west side of the city (see the notes at Isaiah 7:3). Between the two walls for the water of the old pool - Hezekiah built one of these walls himself (2 Chronicles 32:5, 2 Chronicles 32:30; compare 2 Kings 25:5, and Jeremiah 39:4). Between these two walls the water would be collected so as to be accessible to the inhabitants of the city in case of a siege. Before this, the water had flowed without the walls of the city, and in a time of siege the inhabitants would be cut off from it, and an enemy would be able easily to subdue…”

“Thereof - Of Jerusalem, expressed in the foregoing verse. Him - God, who made it a city, and the place of his special presence and worship. Long ago - Which may be added to aggravate their sin, in distrusting that God, who had now for a long time given proof of his care and kindness in defending this city. Isaiah 22:12”

“a ditch: Neh 3:16 ye have: Isa 8:17, Isa 17:7, Isa 31:1, Isa 37:26; Ch2 6:6, Ch2 16:7-9; Jer 33:2, Jer 33:3; Mic 7:7 Isaiah 22:12”