Pictograms
The term rebus also refers to the use of a pictogram to represent a syllabic sound. This adapts pictograms into phonograms. A precursor to the development of the alphabet, this process represents one of the most important developments of writing. Fully developed hieroglyphs read in rebus fashion were in use at Abydos in Egypt as early as 3400 BCE.
The writing of correspondence in rebus form became popular in the 18th century and continued into the 19th century. Lewis Carroll wrote the children he befriended picture-puzzle rebus letters, nonsense letters, and looking-glass letters, which had to be held in front of a mirror to be read. Rebus letters served either as a sort of code or simply as a pastime.
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