Today, when modern mining technology puts salt on our tables virtually free of charge, it's hard for us to imagine how difficult to obtain, and therefore how valuable, this mineral used to be.
And since salt was a vital necessity to every inhabitant, for cooking and preserving food, for tanning leather, and for making gunpowder, alum and glass, salt production was not only a source of income but also an instrument of power. So where possible, countries produced their own salt, the demand for which was enormous.
Polish salt was traditionally the property of Polish kings, who realised right from the start the importance of safeguarding their interests. The deposits at Wieliczka and Bochnia, a few miles to the east, became the Royal Cracow Salt Mines - Poland's oldest state-owned company. Rights of prospecting and operating the mines were leased out to private persons, but the income from the salt belonged to the monarch.
Indeed, the royal monopoly was so successful in some periods that as much as one third of the Crown revenues came from salt. And this was put to good use: building castles and palaces; patronising the arts and sciences; endowing churches, hospitals and seats of learning; bribing the nobility and financing the military. Cracow, they used to say, rested on salt.