Matthew Poole and continuators on Judges 9:45

45 And Abimelech fought against the city all that day, and he took the city, and slew the people that was therein, and beat down the city, and sowed it with salt .

Not to make the place barren, as salt will do, for then he would have sowed the Fields, not the City; but in token of his detestation and desire of their utter and irrecoverable Destruction: for Salt is the symbole or sign of Perpetuity; Compare Numb. 18. 19. Deut. 29. 23. 2 Chron. 13. 5. Zeph. 2. 9.