Upon (rather, over) a wall made by a plumb line. The word translated "plumb line" (anakh) occurs only here. Septuagint ἀδάμας: so the Syriac; Vulgate, trulla caementarii; Aquila, γάνωσις, "brightening," "splendor;" Theodotion, τήκομενον.
As the word in other dialects means tin or lead, it is usually taken here to mean the plumb line which builders use to ascertain that their work is even and perpendiculur. The "wall" is the kingdom of Israel, once carefully built up, solidly constructed, accurately arranged.
God had made it upright; how was it now?