Judges 1:23

And the house of Joseph sent to descry Bethel, a scouting party. (Now the name of the city before was Luz, namely, in ancient times, when the country was still in the hands of the Canaanites.) "As Jebus indicated particularly the fortress, Jerusalem the city although the latter name also embraced both, so a similar relation must be assumed to have existed between Bethel and Luz. Otherwise the border of Benjamin could not have run south of Luz, Joshua 18:13, while nevertheless Bethel was reckoned among the cities of Benjamin, Joshua 18:22. " (Lange.) It was thus the old section of the city, the fortress part, against which the expedition was directed.