Oral tradition holds that the ruling classes were the only ones who could read the tablets, and the ability to decipher the tablets was lost along with them. Numerous attempts have been made to read the tablets, starting from a few years after their discovery. But to this day, none have proven successful. Some authors have proposed that rongorongo may have been an attempt to imitate European script after the idea of writing was introduced during the "signing" of the 1770 Spanish Treaty of Annexation or through knowledge of European writing acquired elsewhere. They cite various reasons including the lack of attestation of rongorongo prior to the 1860s, the clearly more recent provenance of some of the tablets, the lack of antecedents, and the lack of additional archaeological evidence since its discovery. Others argue that it was merely a mnemonic list of symbols meant to guide incantations. Whether rongorongo is merely an example of trans-cultural diffusion, or a true indigenous Austronesian writing system (and one of the few independent inventions of writing in human history) remains unknown and may never be known.