John Gill Commentary 2 Kings 18:8

"He smote the Philistines unto Gaza and the borders thereof, from the tower of the watchmen to the fortified city." — 2 Kings 18:8 (ASV)

He smote the Philistines even unto Gaza, and the borders
thereof
Who in his father's time had invaded Judah, and taken many cities and towns in it, which Hezekiah now recovered, and drove them to their own territories, of which Gaza was one; see (2 Chronicles 28:18)

from the tower of the watchmen to the fenced city ;
that is, places both great and small, cities, towns, and villages; of this phrase, see (2 Kings 17:9) .