Jamieson, Fausset and Brown on 2 Chronicles 25:11

11. valley of salt--This ravine lies to the south of the Dead Sea. The arms of Amaziah, in reward for his obedience to the divine will, were crowned with victory--ten thousand of the Edomites were slain on the field, and as many taken prisoners, who were put to death by precipitation "from the top of the rock" [2Ch 25:12]. This rock might be situated in the neighborhood of the battlefield, but more probably it formed one of the high craggy cliffs of Selah (Petra), the capital of the Edomites, whither Amaziah marched directly from the Valley of Salt, and which he captured (2Ki 14:7). The savage cruelty dealt out to them was either in retaliation for similar barbarities inflicted on the Hebrews, or to strike terror into so rebellious a people for the future. The mode of execution, by dashing against stones (Psa 137:9), was common among many ancient nations.