The text aims to look at the three functions of the Daugava River: border, obstacle, and trade route. We will focus on the river in the Early Modern Period (from the 16th to the 18th century). We will go beyond the chronological framework, during which we will attempt to answer the following questions. Was the border on the Daugava shaped? To what extent was the dividing line permanent? What was the defensive value of the river? Due to the differences during the border and fighting conducted, the river has been divided into two sections: Livonian (today Latvian) and Ruthenian (today Belarussian and Russian). The article is of review character, and the basis for writing this paper is a large amount of literature. In some cases, sources were used, and in exceptional circumstances, we reached for sources. To compare the Daugava River to other rivers, we used the literature on the Vistula, the Volga River, the Dnieper, and the Danube. The border of the Livonian section of the Daugava, which was established in the 16th–18th centuries, survived until the 20th century. It shows the river’s role as a border, which can only be compared with the Danube. Daugava was not an insurmountable obstacle. Most of the fighting was fought near the river, as was the case with the Dnieper and Danube. The rivers compared were also the most important routes in the region. There were natural and institutional obstacles to navigation. We travelled on very similar boats that could be used in military operations. There are differences in the trade of goods. On no other large river, the transport of forest goods was so dominant.