After years of Sufi learning, Dara Shukoh sought to uncover a common mystical language between Islam and Hinduism, boldly stating that the Kitab al-Maknun, or "Hidden Book", mentioned in the Qur'an (56:78) is none other than the Upanishads.

[4] Over a century after the execution of Dara Shukoh, the Sirr-i-Akbar was translated into a mix of Latin, Greek, and Persian by the French traveling Indologist Abraham Hyacinthe Anquetil-Duperron in 1796, titling his version the Oupnek'hat or the Upanischada.

In the spring of 1814, the Latin translation by Anquetil-Duperron caught the eye of German philosopher Arthur Schopenhauer, who heralded the ancient text in two of his books, The World as Will and Representation (1819) and Parerga and Paralipomena (1851), stating: From every sentence deep original and sublime thoughts arise, and a high and holy and earnest spirit pervades the whole.

[5]The impact of the Upanishads on German idealist philosophers such as Schopenhauer and his contemporary Friedrich Wilhelm Joseph Schelling echoed into the United States with the Transcendentalists.

Members of the movement such as Emerson and Thoreau embraced various aspects of the Naturphilosophie invented by Schelling, along with the exotic mysticism found in the Upanishads.