We reproduce here forty previously unpublished letters sent by Jan Patočka to the Polish philosopher Krzysztof Michalski between 1973 and 1976. The letters to Michalski reveal his key role in motivating Patočka to formulate his ideas concerning the philosophy of history and present them first in a series of underground lectures in Prague and finally on paper in his last samizdat book, the Heretical Essays on the Philosophy of History.