The defeat at Poltava in 1709 effectively brought Sweden’s era as a great power to an end. Twenty-three thousand prisoners of war from the Swedish army were scattered across Russia. Their conditions were often extremely harsh. However, the Carolinian prisoners organized themselves, in part by maintaining joint church and school activities. Many individual Carolinians wrote letters and kept diaries, which are available for historians and other researchers to use. It has long been known, however, that numerous letters to and from the prisoners were censored. When the Russian archives were opened in the 1990s, this entirely new source material became accessible. In a previous project, conducted by Sverigekontakt and supported by the Torsten Söderberg Foundation, these letters were traced and digitized, resulting in a now nearly complete collection. This collection also includes previously unknown letters. The purpose of the current project is to further process this collection of letters so that it can be made available to the academic community and the general public. The content of the letters covers a wide range of topics. Given that they were previously inaccessible, they are expected to shed new light on the prevailing conditions at the time. The often well-educated Carolinians contributed to the development of infrastructure in Russia. Before contacts between Sweden and Russia were severed in the winter of 2022, this material also aroused interest in Russia. The new project also sheds light on conditions in Sweden during a decisive period of transition.