The battle for Mariupol was one of the most intense battles in the early phase of the Russian invasion of Ukraine in 2022. While the battle has been called a siege, there is limited research examining how the Russian forces employed siege tactics in order to capture the city. Contemporary warfare is increasingly showing signs that war and conflicts are getting more urbanised. Western militaries and researchers have emphasized combined arms, precision and highly trained forces to acchieve succes in the urban enviroment. However, the war in Ukraine has in several areas been more related to attrition and siege warfare as conducted in the 18th century. The purpose of the study is to contribute to the broader field of reasearch on modern sieges in the urban enviroment and to develop an understanding of the case of Mariupol. More specifically the purpose is to explain how Russsian forces used modern siege tacits in order to capture Mariupol in 2022. The study uses a qualitative case study approach and draws on Nils Hägerdal´s as well as Amos Fox´s theories on modern siege tactics to help explain the case. The results show that in several aspects Russian forces used siege tactics to capture Mariupol. Instead of a direct assault on the city, they began by encircling and isolating both civilans and Ukrainian forces within in the city. After the encirlclment was complete, Russian forces gradually increased pressure on Ukrainan forces through indisrciminate bombardment and repeated assaults. In the end this contributed to gradually minimize the will and resistance of the Ukrainian forces. The Russian use of modern siege tactis thus constitutes a central explanation for how the Russian forces succeded in capturing Mariupol in 2022.