Fausset's Bible Dictionary
("peace".) The oldest name, Jehus the next, Jerusalem ("seeing", or "the foundation of peace") the latest, of Jerusalem. The cities of the plain were probably S. of the Dead Sea; so Salem is Jerusalem, and "the king's dale" the valley of the Kedron. The theory of their being N. of the Dead Sea is what necessitates its upholders to seek Salem far north of Jerusalem (Genesis 14:17-18). But no king of Salem distinct from Jerusalem is mentioned among the kings conquered by Joshua. Moreover, Αdonizedek ("lord of righteousness") king of Jerusalem (Joshua 10:3) was plainly successor of Μelchizedek ("king of righteousness"), it was the common title of the Jebusite kings. Further, "the king's dale" (2 Samuel 18:18), identified in Genesis 14:17 with Shaveh, is placed by Josephus and by tradition (the targum of Onkelos) near Jerusalem (Hebrews 7:1-2). Lastly, Psalm 76 identifies Salem with Jerusalem.
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Fausset, Andrew R. Entry for 'Salem'. Fausset's Bible Dictionary. https://www.studylight.org/dictionaries/eng/fbd/s/salem.html. 1949.