Passing the River Mem is drawn as a glyph-form for the Hebrew letter Mem in the Transitus Fluvii, or Passing the River, one of three magical scripts Heinrich Cornelius Agrippa published in 1533, its name recalling a symbolic crossing of the Euphrates, rather than a script with independent letter meanings of its own; Mem's own sound and classification, discussed elsewhere in this atlas, belong to the underlying Hebrew tradition.
As one of the Sefer Yetzirah's three mother letters, Mem is paired with the element water and, in the same classical scheme, with the belly and a cold climate, the belly being read as the seat of silence and stillness, the passive counterpart to Aleph's breath and Shin's speech. Agrippa printed Transitus Fluvii alongside Celestial and Malachim in Book III of his Three Books of Occult Philosophy, Cologne 1533, without citing a source for any of the three, and no earlier witness to any of them survives; the name, recalling the crossing of the Euphrates, is generally read as a reference to the exodus of Abraham's household out of Mesopotamia, a symbolic passage from an older world into the one Hebrew tradition claims for itself. Of the other two mother letters, Aleph is paired with air and Shin with fire, the three together forming the elemental triad the Sefer Yetzirah builds its whole cosmology upon.