After being crowned as king a third time (2 Samuel 5:1-4), David decides to attack and capture the Canaanite stronghold of Jebus/Jerusalem. This city was more central to the new kingdom than Hebron plus it was on the border of Judah and Benjamin so no Israelite tribe could really claim that it was their own. There may be a third reason for choosing this place: it was the city where Melchizedek was a king-priest (Gen 14:18) and David may already have begun to recognize that he had a large role to play in that line (Psalm 110:1-4).
In 2Sam. 5:8 David mentions attacking the citadel through the “tsinoor,” traditionally rendered as “water shaft.” The LXX reads: καὶ εἶπεν Δαυιδ … Πᾶς τύπτων Ιεβουσαῖον ἁπτέσθω ἐν παραξιφίδι καὶ τοὺς χωλοὺς καὶ τοὺς τυφλοὺς… (And David said… “Anyone who beats the Jebusites should smite the lame and the blind with a dagger”). This translates as “dagger” (παραξιφίδι) the Hebrew noun tsinnor. The Greek word appears to be a neologism (invented by the LXX translators), which only enhances the controversy over the exact meaning of the Hebrew word. I have always taken the passage to refer to Joab’s secretly entering the city through the water system (“Joab’s shaft” - 1Chron 11:6). Maybe the LXX translators were not familiar with the underground water system and understood the tsinnor as a similar Hebrew word for “shield” (tsinah, the suggestion from LEH LXX lexicon).
This certainly is a fascinating passage that will always provide a challenge to both translators and interpreters.