The Persepolis Fortification archive provides new insights into the study of Old Iranian, particularly regarding the debate over the "Median language". The archive contains numerous Iranian names in Elamite transcription, allowing for the identification of phonetic differences between Old Persian and Median names. The high frequency of certain names enables detailed prosopographic analyses, revealing that individuals with varying spellings of their names may in fact be the same person. This is illustrated by the case of Ziššawiš, a vice director and deputy satrap in Persepolis. The variations in the spelling of his name suggest dialectal differences within the Persian heartland. While the accuracy of spelling was likely high, all variations were allowed, indicating that Median should be viewed as a dialect rather than a separate language.