Albert Barnes Commentary 1 Kings 20:30

"But the rest fled to Aphek, into the city; and the wall fell upon twenty and seven thousand men that were left. And Ben-hadad fled, and came into the city, into an inner chamber." — 1 Kings 20:30 (ASV)

A wall — This refers to "the wall," that is, the wall of the town. We may suppose that a terrific earthquake occurred during the siege while the Syrians were manning the defenses in full force. The quake threw down the wall where they were most thickly crowded, burying them in its ruins.

Ben-hadad fled from the wall, where he was at the time of the disaster, into the interior of the city. There he concealed himself, probably in some massive stronghold.