Referral Back to Previous Conquests by Judah in the Time of Joshua (Judges 1:10-20).
‘ And Judah went against the Canaanites who dwelt in Hebron. Now the name of Hebron was previously Kiriath-arba. And they slew Sheshai, and Ahiman, and Talmai '
The first attack was on the hill country. Hebron was first taken by Joshua, and the inhabitants put to the sword (Joshua 10:36-39), but while Joshua was employed in making other conquests, the Canaanites who had fled into the mountains clearly took possession of it again. Thus it had to be re-subdued. This kind of situation occurred regularly. Joshua's onslaught was in order to gain a firm foothold in the land, but the occupation of all cities permanently would take more time. It was an art that had to be learned.
In this case the re-conquest took place through Caleb while Joshua was still alive. It was referred to as being carried out by Joshua as the overall commander-in-chief in Joshua 11:21-23, but this does not prevent it having been done by Caleb, for he was acting under Joshua's leadership. The reason it is described here is that it is seen as being part of Judah's total conquest of his portion. The writer was not so much concerned with chronology as giving a total picture (the lack of interest in chronology of Israel comes out in that their verbal system was only able to express it imperfectly. For example, they had no pluperfect. Their tenses indicated either completed or incompleted action. What mattered to them was that things were done, not when they were done).
Hebron had been granted to Caleb, the son of Jephunneh the Kenizzite (Numbers 32:12; Joshua 14:13) who was associated with Judah (Joshua 15:13), and he then proceeded to take it as described here and in Joshua 15:13-19. Some would see this as indicating a Kenizzite invasion from the south not directly connected with the Israelite invasion, but there is nothing in the text to suggest it. When ‘Israel' came out of Egypt they were made up of many nations (Exodus 12:38), which would include Kenizzites, natives of Canaan (Genesis 15:19), who had sought refuge at some time in Egypt. It is far more likely that such people, participating in the exodus, would become worshippers of Yahweh, than that a Canaanite tribe invading on their own would.
“Now the name of Hebron was previously Kiriath-arba.” (‘The city of four' or ‘the city of Arba') - see Genesis 23:2. According to Joshua 14:15 LXX it was the ‘mother-city of the Anakim'. There is no reason to doubt that Arba was a name as suggested there, and it was certainly related to the Anakim in some way in the Hebrew text which may suggest it was named after a famous ancestor of the Anakim, possibly named Arba because he had the strength or usefulness of four men.
“And they slew Sheshai, and Ahiman, and Talmai.” These were children of the Anakim (Numbers 13:22), outsized men and leaders who were renowned fighters (Deuteronomy 9:2).