What were strongholds?
In ancient times civilizations would build strongholds as fall-back points. When an enemy army invaded in such force that they either defeated a nation’s army or could not even be met on the field of battle everyone would abandon their unprotected villages and fall back to strongholds.
We find a mention of strongholds in Judges when the Midianites were invading, filling the land like grasshoppers. The Israelites built themselves strongholds in the mountains. Invading armies could strip the land of its crops, pillage and burn the villages, but behind the high walls and towers of these craggy fortresses the people would survive. And as long as the people survived so would the nation.