This article contains the text of a letter from the Hungarian and German king, Sigismund of Luxemburg, to the commune of Caffa, a Genoese colony in Crimea. In his struggle against Venice, the king hoped for the help of Genoa, which competed with the Republic of Venice in the Levantine trade. To undermine Venetian trade routes, Sigismund hoped to both establish contact with the Horde’s khan, Jalal ad-Din, with the mediation of Caffa’s administration, and to restore the transit trade of expensive Oriental goods from China to the Danube and further into Hungary and Germany. To this end, an official Hungarian embassy was sent to Caffa in 1412. The letter rather meagerly reflects the opinion of the king regarding the distant Horde and its rulers. However, the circumstances of the embassy make it possible to understand the broader European context of Sigismund’s eastern policy, which in one way or another affected Genoa, the Ottoman Empire, and the Polish Kingdom. The published source is of considerable interest to researchers of the history of the Horde, the Crimea, and the Genoese colony of Caffa, taking into account the fact that Sigismund tried to implement his anti-Venetian plan in 1418 and possibly once again between 1419 and 1428, and given the scarcity of information on the Hungarian-Tatar relations in the early fifteenth century. Thus, this article contains the Latin text of the letter and its Russian translation as well as an introduction which highlights the context of events both in Hungary and the distant Venetian colony of Tana (Tatar: Azaq), located at the mouth of the Don.