This article analyzes the diplomatic and military relations between the Sasanian Empire and the Roman and Byzantine Empires from the third to the seventh centuries AD based on historical sources. The study examines the main directions of Sasanian foreign policy, military campaigns, and diplomatic agreements with reference to specific dates. Particular attention is given to the reigns of Shapur I, Shapur II, Khosrow I Anushirvan, and Khosrow II Parviz. The geopolitical significance of Mesopotamia, Armenia, the Caucasus, and Syria is explored, as well as the consequences of competition for control over these regions. The findings help to assess the regional influence of Sasanian foreign policy and its role in the system of late antique international relations.