Salt is common, easy to obtain and inexpensive. It is the stuff of kitchens and cooking. Yet trade routes were established, alliances built and empires secured – all for something that filled the oceans, bubbled up from springs, formed crusts in lake beds, and thickly veined a large part of the Earth’s rock fairly close to the surface. From pre-history until just a century ago – when the mysteries of salt were revealed by modern chemistry and geology – no one knew that salt was virtually everywhere. Accordingly, it was one of the most sought-after commodities in human history. Even today, salt is a major industry. Canada, Kurlansky tells us, is the world’s sixth largest salt producer, with salt works in Ontario playing a major role in satisfying the Americans’ insatiable demand.