A picture here does the work of an armed guard. In the 1922 collection Myths & Legends of China, the Emperor T'ai Tsung of the T'ang dynasty falls ill and "imagined that he heard demons rampaging in his bedroom". Two of his ministers, Ch'in Shu-pao and Hu Ching-tê, offer to "sit up all night and watch outside his door"; standing fully armed at the palace gate, they hold the night off, and "the Emperor slept in peace." Unwilling to wear his living guards out forever, he has them "paint their portraits in full martial array" and paste the images on the doors — and the painted men keep the very same watch: "For some nights all was peace".

Behind this lies an older layer the same witness preserves. On a vast peach-tree by the Eastern Sea, two spirits, "Shên Shu (or Shu Yü) and Yü Lü", guarded the Door of the Devils (kuei); wrongdoers were "given over to be devoured by tigers". The emperor Huang Ti had "the portraits of the two spirits painted on peach-wood tablets" hung above his doors to turn evil back — and from that, the record says, came the coloured mên shên (door-gods) "on almost every door in China."

What both tellings share is the strange confidence that a likeness carries the authority of the thing it shows: a portrait of a guardian is itself a guardian, a painted spear enough to stop a real demon. The shelf gives this one Chinese witness in full and vivid detail. At what point does a picture of a watchman stop depicting the watch and begin to stand it?