Charles Ellicott Commentary 1 Kings 16:18

"And it came to pass, when Zimri saw that the city was taken, that he went into the castle of the king`s house, and burnt the king`s house over him with fire, and died," — 1 Kings 16:18 (ASV)

The palace of the king’s house. —The same phrase is found in 2 Kings 15:25. The word here rendered “palace” evidently means (as is clear from its derivation) “the high place,” or “citadel,” of the building. Some render it the “harem,” with which the curious rendering (ἄντρον) of the Septuagint—signifying properly a cave or “lurking-place”—may perhaps agree. But this is not suggested by the word itself.

This desperate act of Zimri, which has many parallels in Eastern history, seems to indicate that there was held to be something especially treasonable, and therefore unpardonable, in his assassination of Elah. (See 1 Kings 16:20, and 2 Kings 9:31.)