The defeat at Poltava in 1709 largely ended Sweden's period of great power. 23 000 prisoners of war from the Swedish army were scattered across Russia. Conditions for them were often very difficult. However, the Carolingian prisoners organized themselves, for example by maintaining joint church and school activities. Many individual Carolinians wrote letters and diaries, which are available for historians and other researchers to use. However, it has long been known that many letters to and from prisoners were censored. When the Russian archives were opened in the 1990s, this brand new source material became accessible. In an earlier project, conducted by Sverigekontakt and supported by the Torsten Söderberg Foundation, these letters have been traced and digitized, so that an almost complete collection now exists. This also includes previously unknown letters. The aim of the current project is to further process this collection of letters so that it can be made available to the research community and the general public. The content of the letters covers a wide range of topics. Given that they were previously inaccessible, they can be expected to shed new light on the conditions prevailing at the time. The often well-educated Carolinians contributed to the building of infrastructure in Russia. Before the breakdown of contacts between Sweden and Russia in the winter of 2022, this material also attracted interest in Russia. The new project also sheds light on conditions in Sweden during a crucial period of transition.