Commentators explain that 'Sheshach' is a code name for Babylon. Most scholars, like Calvin and Gill, believe it was created using a Hebrew cipher called 'athbash,' where the last letter of the alphabet is substituted for the first, the second-to-last for the second, and so on. This literary device adds a layer of style while the parallel use of 'Babylon' in the same verse makes the meaning clear.