Jerusalem is built as a city that is compact together:
All Commentaries on Psalms 122:3 Go To Psalms 122
George Leo Haydock
AD 1849
Together. Well built and inhabited. The Jews throughout the world considered it as their most dear country. (Calmet)
The participation of spiritual graces (Psalm cxviii. 63.) is a great comfort to Catholics, (Worthington) who look upon the chair of St. Peter at Rome as the centre of unity. (Haydock)
David established order in Jerusalem, when he had made the conquest, and various families contributed to the rebuilding of it. (Berthier)
All the tribes were united under the dominion of David. (Houbigant)