Albert Barnes Commentary 2 Kings 15:14

"And Menahem the son of Gadi went up from Tirzah, and came to Samaria, and smote Shallum the son of Jabesh in Samaria, and slew him, and reigned in his stead." — 2 Kings 15:14 (ASV)

Tirzah, the old capital, once more appears as a place of importance, giving birth to the pretender, who alone of all these later kings died a natural death and left the crown to his son (2 Kings 15:22). It would seem from the present passage that it was on lower ground than Samaria.