Now these are the nations which Yahweh left, to prove Israel by them, even as many [of Israel] as had not known all the wars of Canaan;
"The five lords of the Philistines"  (Judges 3:3).  These were the rulers of Gaza, Ashdod, Ashkelon, Gath, and Ekron.  At first, Israel occupied some of these cities (see under  Judges 1:18), but these enemies of Israel were able to re-take their territory from Israel as late as the times of Saul, whose kingdom they defeated, killing the monarch himself.