Van Loon would playfully draw visual metaphors, typically on his maps. These were objects meant to symbolize some historical phenomenon, for example, a cauldron in the middle of Mesopotamia as a way to symbolize “The Melting Pot of the Ancient World,” a wall or fence to represent the boundaries of an empire, or the branches of a tree to show the spread of a word into different languages.

"Mesopotamia, the Melting-pot of the Ancient World," p. 30

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