Salting the earth

Salting the earth refers to the practice of spreading salt on fields to make them incapable of being used for crop-growing. This was done in ancient times at the end of some wars as an extremely punitive scorched earth tactic.

Examples

The Assyrians are described in ancient records as salting the capitals of neighboring countries which repeatedly rebelled against paying them tribute—including Mitanni in c. 1290 BC, and centuries later, Elam in c. 640 BC.

According to the Book of Judges (9:45) in the Old Testament, Abimelech, the judge of the Israelites, sowed his own capital, Shechem, with salt, ca. 1050 BC, after quelling a revolt against him.

One example of salting the earth supposedly occurred at the end of the Third Punic War in 146 BC between the Roman Republic and Carthage. After sacking the city of Carthage and forcing the few survivors into slavery, an area 50 miles around the city was reportedly salted. The historical verifiability of this event is often questioned: salting such a vast region would have required a tremendous amount of salt, a substance so valuable that it was sometimes used as money — although it is well known that the Phoenicians themselves were among the first to produce salt cheaply, by simply evaporating seawater. Aside from the logistics involved, the first reference to the Roman salting of Carthage is found in the 19th century German historian Ferdinand Gregorovius, in History of the City of Rome in the Middle Ages — making it highly likely that the story is a later fabrication. Moreover, such an action would have hindered Rome's subsequent growth and development, which relied heavily on grain imported from North Africa.

In Spain and the Spanish Empire, salt was poured onto the land owned by a convicted traitor (often one who was executed and his head placed on a picota, or pike, afterwards) after his house was demolished. The practice was abandoned in the 17th century.
Stone memorial to the Duke of Aveiro's punishment in Belém, Lisbon. The markings on the side are vandalism with spraypaint

Likewise, in Portugal, salt was poured onto the land owned by a convicted traitor. The last known event of this sort was the destruction of the Duke of Aveiro's palace in Lisbon in 1759, due to his participation in the Távora affair (a conspiracy against King Joseph I of Portugal). His palace demolished and land salted, a stone memorial now perpetuates the memory of the shame of the Aveiros, where it is written (English translation):

In this place were put to the ground and salted the houses of José Mascarenhas, stripped of the honours of Duque de Aveiro and others, convicted by sentence proclaimed in the Supreme Court of Inconfidences [IE. Conspiracies] on the 12th of January 1759. Put to Justice as one of the leaders of the most barbarous and execrable upheaval that, on the night of the 3rd of September 1758, was committed against the most royal and sacred person of the Lord Joseph I. In this infamous land nothing may be built for all time.

Modern usage

Today the term is used in a variety of ways, referring in general to any sort of poisoning. This varies from the direct use of area denial weapons or radiological weapons, to the philosophical, where it is often used to describe business strategy to avoid takeovers (similar to but broader in scope than a poison pill).