‘Then Horam king of Gezer came up to help Lachish, and Joshua smote him, and his people, until he had left him none remaining.'
When Horam, king of Gezer, heard that Lachish was being attacked (they may well have had a mutual help pact) he hastened to help them. But he arrived too late and found himself having to face Israel alone. The result was that he was slain and his army decimated. Joshua must have been a brilliant general. But Gezer was a strong city and never fully occupied by Israel, although later subjected to taskwork (Joshua 16:10). It was later captured by Merenptah of Egypt and then by the Philistines, being given by Egypt to Solomon on his marriage.
Gezer was on the northern ridge of the Shephelah, overlooking the Valley of Aijalon, a few miles from the main coastal highway between Egypt and the north. It had been taken by the Egyptians in the 15th century BC, and is mentioned as remaining loyal (if vacillating) in the Amarna letters. But at this stage it appears to have been at least semi-independent. As mentioned it was later taken by Merenptah while the Israelite occupation was still under way. It would later be occupied by the newly arriving Philistines, possibly with Egyptian consent.