A history of human exchange. From Barter: "The armour of Diomede, says Homer, cost only 9 oxen; but that of Glaucus cost a hundred oxen", to the modern money economy and digital banking. How was currency debased then, and how is it done today? + Money assumes private property and a division of labour, so cannot exist in a pure socialist society. I didn't mention it here much, but Lenin's attempts to abolish money and the progressive return to the NEP's use of a gold standard make for remarkable reading.