The article is devoted to the designating the Achaemenid Empire in old Persian royal inscriptions. The article demonstrates that in Achaemenid inscriptions the Persian Empire was perceived as a conglomerate of countries (dahyāva), in which a special place was given to the region of Parsa (dahyāṷš Pārsa), in which Darius I called himself king (xšāyaϑiya Pārsai̯). Darius calls himself both “king in Persia” and “king of countries” only in the Behistun inscription; in subsequent texts in Old Persian he calls himself the king of many countries (xšāyaϑiya dahyūnām tayai̯šām parūnām), the king of the countries of all nations (xšāyaϑiya dahyūnām vispazanānām), or the king of the countries of many nations (xšāyaϑiya dahyūnām paruzanānām). The inscriptions emphasize the king's power over the entire earth (būmi-), created by Ahuramazda, over all or many peoples included in the countries subject to the king. The concept of kingdom (xšaça-) is also reflected in the inscriptions, in which the word xšaça- means both kingdom and kingship. However, the contexts where xšaça- is used demonstrate a more precise meaning of the word. The inscriptions state that Ahuramazda bestowed royal power and kingdom on the ruler, however, power over the kingdom received from the god meant the right to rule the territory. The Great King himself had to make certain efforts to protect the kingdom, as becomes obvious from the story in the Behistun inscription about the seizure of the kingdom by the magician Gaumata and the subsequent return of it by Darius to his legitimate authority.