He spent three years in Paris and London, engaged in copying and collating manuscripts, and collecting materials for future research, especially with reference to Hindu drama and philosophy.
His Anthologia Sanscritica, which came out the following year, contained several hitherto unpublished texts, and did much to stimulate the study of Sanskrit in German universities.
In his Beiträge zur Deutung der Eugubinischen Tafeln (1833) he prepared the way for the correct interpretation of the Umbrian inscriptions; and the Zeitschrift für die Kunde des Morgenlandes (7 vols., 1837–1850), started and largely conducted by him, contains, among other valuable papers from his pen, grammatical sketches of the Beluchi and Brahui languages, and an essay on the Lycian inscriptions.
[3] Soon after the appearance of Burnouf's Commentaire sur le Yacna (1833), Lassen also directed his attention to the Zend language, and to Iranian studies generally; and in Die altpersischen Keilinschriften von Persepolis (1836) he greatly improved the knowledge of the Old Persian cuneiform inscriptions, following the early efforts of Grotefend (1802) and Saint-Martin (1823).
[4] thereby anticipating, by one month, Burnouf's Mémoire on the same subject, while Sir Henry Rawlinson's famous memoir on the Behistun Inscription, though drawn up in Persia, at about the same time, did not reach the Royal Asiatic Society until three years later, 1839.
He succeeded in fixing the true values of nearly all the letters in the Persian alphabet, in translating the texts, and in proving that the language of them was not Zend, but stood to both Zend and Sanskrit in the relation of a sister.The first successful attempts at deciphering the Brahmi script were made in 1836 by Christian Lassen, who used a bilingual Greek-Brahmi coin of Indo-Greek king Agathocles to correctly identify several Brahmi letters.
[10] He contemplated bringing out a critical edition of the Vendidad; but, after publishing the first five fargards (1852), he felt that his whole energies were required for the successful accomplishment of the great undertaking of his life—his Indische Altertumskunde.
In this work—completed in four volumes, published respectively in 1847 (2nd ed., 1867), 1849 (2nd ed., 1874), 1858 and 1861—which forms one of the greatest monuments of untiring industry and critical scholarship, everything that could be gathered from native and foreign sources, relative to the political, social and intellectual development of India.