Next to learning the Persian, Kannada and Hindustani languages, Roth at Agra for several years also acquired a profound knowledge of classical Sanskrit grammar and literature from local pandits.
The French explorer and philosopher Francois Bernier, who got acquainted with Roth in these years, got to appreciate him as one versed in expert knowledge of the culture and philosophy of religions in India[3] In 1662, joined by fellow Jesuit Johann Grueber, who was on his way back from China, Roth revisited Europe by the land route via Kabul, and arrived in Rome in February 1664.
[4] Traveling north to Germany, Roth held some public lectures in Neuburg on the history and culture of the Mughal Empire, excerpts of which subsequently appeared in print.
[8] Heinrich Roth's Sanskrit grammar, that he had completed by 1660 in Latin language under the title Grammatica Linguae Sanscretanae Brachmanum Indiae Orientalis (the manuscript of which is preserved today at the Biblioteca Nazionale Centrale in Rome) and that was augmented by preliminary studies for a complete Sanskrit-Latin dictionary, made him a pioneering scholar in modern Sanskrit studies in Europe.
Also, a total of 35 letters, written by Roth from India and during his travel back to Europe, survive at the Royal Library of Belgium in Brussels.