The Celestial Language examines how Iranian Shi‘i reformers and Indian Zoroastrian missionaries in the 19th century pursued a vision of “truth” through a reconstructed Persian cosmology. Both groups believed that their foundational texts had been destroyed or altered by early Muslim caliphs in an effort to erase references to ‘Ali, the first Shi‘i Imam, and to suppress ancient Zoroastrian and Persian scientific writings. This shared perception of a “suppression of texts” united Indian Zoroastrians and Iranian Shi‘i Muslims and Zoroastrians in a common effort to reclaim their lost heritage. Rather than opposing Islam, the Zoroastrian missionaries advocated a reinterpretation that emphasized the continuity between Zoroastrian and Islamic principles, placing Islamic cosmology within the broader framework of Persian esotericism. For Iranian reformers, the absence of authoritative texts was not merely an obstacle but an impetus to reimagine Persian identity and reclaim a “truth” believed to have been concealed or lost. Iranian reformers were inspired by a sacred text known as the Dasātīr, believed to have been written in a celestial language attributed to ancient Persian sages and accompanied by a Persian commentary. They studied this text, along with several others written about it in India between the 17th and 18th centuries, to reimagine the relationship between celestial and terrestrial realms. In doing so, they forged a new Persian scientific culture that viewed the revival of Persian spiritual wisdom and scientific progress as a simultaneous and intertwined process. This project emphasizes how Iranian thinkers remembered the past to inspire cultural pride and intellectual advancement, ultimately forming a unique hybrid identity that honoured both their spiritual heritage and scientific achievements.