Charles Ellicott Commentary 2 Kings 23:13

"And the high places that were before Jerusalem, which were on the right hand of the mount of corruption, which Solomon the king of Israel had builded for Ashtoreth the abomination of the Sidonians, and for Chemosh the abomination of Moab, and for Milcom the abomination of the children of Ammon, did the king defile." — 2 Kings 23:13 (ASV)

The high places that were before the city ... —See 1 Kings 11:5–8. “Before” means “to the east of,” because, to determine the cardinal points, one faced the sunrise. The right hand was then the south, the left hand the north, and the back the west.

The mount of corruption. —The southern summit of the Mount of Olives was so-called, because of the idolatry there practiced. It still bears the name of the “Hill of Offence,” derived from the Vulgate “mons offensionis.” (The word rendered “corruption,” mashhîth, may originally have meant “anointing,” from mâshah “to anoint,” and have simply referred to the olive oil there produced. The name would thus be equivalent to the German Oelberg. In later times the term was so modified as to express detestation of idol-worship.)

Did the king defile. —As it is not said that they were pulled down, these high places may have been merely sacred sites on the mountain, consisting of a leveled surface of rock, with holes scooped in them for receiving libations, etc. Such sites have been found in Palestine; and it is hardly conceivable that chapels erected by Solomon for the worship of Ashtoreth, Chemosh, and Milcom, would have been spared by such a king as Hezekiah, who even did away with the high places dedicated to Jehovah (2 Kings 18:3).