For thou hast been a Shelter for me. In the past thou hast often been my "Shelter" or my "Refuge" (comp. Psalms 18:2; Psalms 44:7, Psalms 44:11; Psalms 48:3, etc.); be so once more. And a strong Tower.
A migdal—a fortress, like the great fortress of the south (Exodus 14:2)—the Magdolus of Herodotus (2.149). From the enemy. If the psalm is David's, "the enemy" is probably Absalom.