2 Chronicles 26:6
"And he went forth and warred against the Philistines, and brake down the wall of Gath, and the wall of Jabneh, and the wall of Ashdod, and built cities about Ashdod, and among the Philistines."
The Philistines were always the nagging enemy of the children of Israel. Every king of Israel had to deal with this country, and they were never truly able to destroy them. Yet, you will find that there were kings who conquered them at times, and Uzziah was one of those kings.