Tonight's episode takes us on a historical tour of salt: how much is there on Earth? Why did it start to be an important commodity for humans in the Neolithic? How was it extracted and transported in ancient times? We will explore all this, and more: how the taxation of salt helped early states to function, how salt was extracted and transported in medieval times, the history of various food preservation methods using salt, and how it was partially replaced with other techniques such as canning and refrigeration.