In this article, the author reviews the key activities of Archimandrite Antonin (Kapustin), who served as Rector of the Russian embassy church in Athens in 1850-1860. The author describes religious and political life in Athens in the mid-19th century on the basis of published sources and yet unpublished materials: Fr. Antonin’s diaries and his reports to the Holy Synod. The author draws particular attention to the constructions of the Russian church in Athens, as well as Fr. Antonin’s views about the relationship of the Russian Church with the Greek Orthodox world.