When did he bring Galyus' head to Yerushalayim?
Radak: After he brought it in front of Sha'ul (verse 57), he brought it to cities of Yisrael, to inform [about Galyus' death] women, children and men who were not at the war, and then he brought it to Yerushalayim.
Why did he bring Galyus' head to Yerushalayim?
Radak citing his father: 'Yerushalayim' refers to Nov the city of Kohanim; we find that Galyus' sword was there (21:10).
Alshich: It was in order to thank Hashem. 1
Metzudas David: It was to inform people [about Galyus' death].
Malbim: It is near Giv'as Sha'ul; David had gone to Giv'as Sha'ul with Sha'ul.
What was special about Yerushalayim? Zevachim 54b says that [later,] when David went to Shmuel in Nayos (19:18), they probed where will be the Beis ha'Mikdash. This implies that now, he did not know that it will be in Yerushalayim! (PF)
It says "he put [Galyus'] Kelim in his tent", but we find that Galyus' sword was in Nov (21:10)!
Malbim: Afterwards it was brought to Nov to recall the miracle.
