looking at sophie 's substitution matrix , langdon felt a rising thrill that he imagined must have rivaled the thrill felt by early scholars when they first used the atbash cipher to decrypt the now famous mystery of sheshach.for years , religious scholars had been baffled by biblical references to a city called sheshach.the city did not appear on any map nor in any other documents , and yet it was mentioned repeatedly in the book of jeremiah - the king of sheshach , the city of sheshach , the people of sheshach .