In Księgi hetmańskie [Hetman Books] by Stanisław Sarnicki, the Ruthenian land of the former Polish-Lithuanian Commonwealth is depicted as a turbulent land under permanent threat. The reason of the threat were the incessant invasions of the Tartars. According to the words of Sarnicki, the inspiration to write the Books were some talks resulting from the activity of the Crimean warriors which were held in Ruthenia. They concerned the issues of war and defense. In his work the author tried to describe precisely the routes of Tartar invasions passing through Ukraine. He paid close attention to the vocabulary used in those territories. He described the bravery of the Ruthenians, their weaponry and methods of combat. He enumerated many well-known people related to the Ukrainian region. In Hetman Books one can also find some information on medicaments used in Ukraine. Sarnicki also devoted a lot of space to the Cossacks, whom he considered great soldiers. He praised their skills of fi ghting in sea battles. He also saw a possibility to establish a Cossack fl eet for the Commonwealth.