The Great Cipher was elusive to even the greatest scholars for more than two centuries, creating a whole span of encrypted letters containing enigmatic answers to some of the biggest speculations in history. When the breakthrough in the pattern of the cipher came in 1983 at the hands of Bazeries, the reasons the cipher was exponentially difficult to crack were revealed.
Not only did Bazeries discover that there were 587 different numbers in total, but he also learned after painstaking exploration that the numbers were not homophones. The simple fact that the Great Cipher did not follow the common practice of substituting one or multiples numbers for a single letter further complicated the ability for cryptanalysts to crack it. Furthermore, the Great Cipher was additionally not combinations of double letters indicated by numbers, but instead contained numbers that represented the syllables in the French language.
The Rossingols were not secure in simply allowing numbers to represent syllables. To further complicate the cipher, the number of digits in the numbers representing each syllable did not correspond to the number of letters in each syllable. For example, in the first word Bazeries decrypted, "les ennemis," while the three digit number 124 represents the syllable "les", three digit numbers also represent "ne" and "s", 125 and 345, respectively. The Rossingols additionally created numbers that represented not a syllable, but deletion of the previously stated syllable.
Together with the death of the Rossingols before the secrets of the cipher could be revealed, these factors created an entirely secure cipher. One so secure it would take the human race an additional two hundred years of discovery to crack.