The name of the city is first mentioned by Xenophon in his expeditionary logs in Achaemenid Assyria of 401 BC, during the reign of the Persian Achaemenid Empire. There, he notes a small Assyrian town of "Mépsila" () on the Tigris somewhere about where modern Mosul is today ("Anabasis", III.iv.10). It may be safer to identify Xenophon's "Mépsila" with the site of Iski Mosul, or "Old Mosul", about north of modern Mosul, where six centuries after Xenophon's report, the Sasanian Empire's center of Budh-Ardhashir was built. Be that as it may, the name Mepsila is doubtless the root for the modern name.