ENIn the late 15th and early 16th centuries, the southeastern borderlands of the Polish-Lithuanian Commonwealth faced intense Tatar and Moldavian raids. This region was sparsely urbanized, complicating its defense. To secure the border, the military was compelled to create a form of military settlement that functioned as a substitute for a city. From around 1479, with the establishment of the so-called ‘Defense of the Borderlands’ (obrona potoczna), the army began to regularly station in semi-permanent field camps. This arrangement was advocated by military theorists of the time, such as Jan Tarnowski, Marcin Bielski, and Stanisław Sarnicki. An analysis based on archival materials reveals that nearly continuously, one or two military camps operated in the borderlands, becoming the largest population centers in these areas. The regular social and economic interactions between the military and local inhabitants were crucial for urbanization. At the same time, these interactions led to the exploitation of resources and ecological degradation. Due to strategic needs and environmental impact, camps were frequently relocated. Military camps were not merely military phenomena but also catalysts for economic development. They had demographic implications as well, with soldiers coming from all over the Kingdom of Poland and the Grand Duchy of Lithuania, often resulting in permanent migrations. Military activities were also linked to state investments in infrastructure. For example, in the 1560s, military expenditures consumed 76% of all revenues and credits of the Grand Duchy of Lithuania.