Jamieson, Fausset & Brown

Ye have seen--rather, "Ye shall see." city of David--the upper city, on Zion, the south side of Jerusalem (Sa2 5:7, Sa2 5:9; Kg1 8:1); surrounded by a wall of its own; but even in it there shall be "breaches." Hezekiah's preparations for defense accord with this (Ch2 32:5). ye gathered--rather, "ye shall gather." lower pool--(See on Isa 22:11). Ye shall bring together into the city by subterranean passages cut in the rock of Zion, the fountain from which the lower pool (only mentioned here) is supplied. See on Isa 7:3; Kg2 20:20; Ch2 32:3-5, represent Hezekiah as having stopped the fountains to prevent the Assyrians getting water. But this is consistent with the passage here. The superfluous waters of the lower pool usually flowed into Hinnom valley, and so through that of Jehoshaphat to the brook Kedron. Hezekiah built a wall round it, stopped the outflowing of its waters to debar the foe from the use of them, and turned them into the city.