#OTD in 1822.
The Rosetta Stone was deciphered by Jean-François Champollion.
Major advances in the decoding were recognition that the stone offered three versions of the same text (1799); that the Demotic text used phonetic characters to spell foreign names (1802); that the hieroglyphic text did so as well, & had pervasive similarities to the Demotic (1814); & that phonetic characters were also used to spell native Egyptian words (1822–1824).