This article is about T. Hartmann — Rakhmaninov’s contemporary and devotee, an outstanding composer, whose body of works is unfortunately completely forgotten. The epistolary intercourse with Hartmann survived among Rakhmaninov’s legacy and it shows how much they have in common. Hartmann, like Rakhmaninov, took theory lessons from A. Arensky and S. Taneev. Their biographies also share a lot — both had to leave Russia, moving to Europe, and then to emigrate to USA. This publication is based upon archival collections.