While the shapes of some Old Persian letters may look similar to signs in Sumero-Akkadian Cuneiform, it is clear that only one of them, LA, was borrowed from Sumero-Akkadian Cuneiform LA, and that because LA is a foreign sign used to represent a sound not used in the Old Persian language. Scholars today agree that the character inventory of Old Persian was newly-invented for the purpose of providing monumental inscriptions of the Achaemenid king, Darius I, by about 525 BCE.
Old Persian is written from left to right. The repertoire contains 36 signs which represent consonants, vowels or sequences of single consonants plus vowels, a set of five numbers, one word divider, and eight ideograms. It is unlikely that more than the characters known today will ever be discovered.