Salmi 31:21

Benedetto sia il SIGNORE, perché mi ha mostrato la sua meravigliosa benignità in una città forte.

Strong city. Yahweh Himself, with His almighty protection, is the "strong city" (Salmi 46:1; Salmi 46:11). Thus, this last verse of the third strophe corresponds to the first verse of the first strophe, Salmi 31:2 (cf. Geremia 18:1).