Isaiah 49:16, New American Standard Bible (NASB):
16 “Behold, I have inscribed you on the palms of My hands; Your walls are continually before Me."
Contextually, Isaiah 49 is describing the return of Jacob/Israel from exile. Verse 49.5:
This includes the rebuilding of the city Jerusalem/Zion. Beginning in verse 14:
The 'walls' are actual walls, which surround the rebuilt Jerusalem/Zion.