The square can be divided into two diagonal
triangles. Because the length of these shapes has no simple relationship
to its sides, the Greeks concluded that the diagonal must be a symbol
of the irrational. Therefore, the diagonal, or oblique, has come to be
associated with the incomprehensible, occult world. In J. K. Rowling’s
Harry Potter books, Diagon Alley is the hidden part of London that is a
magical high street full of occult devices.
