letter frequencies

The frequency of letters in text has been studied for use in cryptanalysis, and frequency analysis in particular, dating back to the Iraqi mathematician Al-Kindi (c. 801–873 CE), who formally developed the method (the ciphers breakable by this technique go back at least to the Caesar cipher invented by Julius Caesar, so this method could have been explored in classical times). Letter frequency analysis gained additional importance with the development of movable type in Asia in 1040 CE and in Europe in 1450 CE, where one must estimate the amount of type required for each letterform, as evidenced by the variations in letter compartment size in typographer's type cases.