It has often been said that the Chinese invented ice cream and that marco polo brought the idea to Europe in the thirteenth century. This is more myth than historical fact backed by evidence but it can be sated with some confidence that ice cream was invented in China in the first milenium. The process of freezing liquids by immersing them in a mixture of ice and salt, which react together to lower the temperature of the mixture below freezing point, was also invented in the distant past - it was first documented in the thirteenth century. This is how ice cream had to be made until the invention of the freezer in the twentieth century. A vessel containing ice and salt surrounds a container containing the ice cream mixture. The temperature in the ice and salt mix drops, freezing the container's contents. To ensure it freezes evenly, it is generally stirred or rotated.