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Food preservation goes back to the last Ice Age, about 15,000 BC, when Cro-Magnon humans discovered for the first time a way of preserving food by smoking it. The evidence for this lies in the caves at Les Eyzies in the Dordogne in France, where this way of life is well portrayed in carvings, engravings and paintings. From then to the present day, heat remains one of the principal cornerstones of food preservation. More complex forms of food processing emerged in ancient and medieval times: baking bread, producing cheese, wine, sun-dried or vinegar-pickled vegetables, and salted or smoked meat. Processed foods made up a significant part of the human diet whenever it was not possible to eat fresh or to be sustained by agriculture and farming due to seasonal changes, crop failures or wars. Marching armies and sailors on long sea voyages relied heavily on processed foods as well. Mass scale food processing (producing foods in large amounts) was introduced during the industrial revolution in the 18th and 19th century, starting with the advent of canned and pasteurised foods. In the first half of the 20th century, the world was ravaged by malnutrition (undernutrition), caused by poverty, an economic depression and two catastrophic world wars. As a result, mass food production focused on sustaining population; reducing foodborne diseases, malnutrition and nutrient deficiencies by providing protein-rich, energy-dense and fortified foods (with vitamins) that were accessible to all.