The event was truly awful. This slaughter is the greatest that we ever read of in sacred history.
2 Chronicles 13:16-19
16 And the children of Israel fled before Judah: and God delivered them into their hand.
17 And Abijah and his people slew them with a great slaughter: so there fell down slain of Israel five hundred thousand chosen men.
18 Thus the children of Israel were brought under at that time, and the children of Judah prevailed, because they relied upon the LORD God of their fathers.
19 And Abijah pursued after Jeroboam, and took cities from him, Bethel with the towns thereof, and Jeshanah with the towns thereof, and Ephrain with the towns thereof.