<p>The city of Ḫarrān in northern Syria, the northernmost part of Mesopotamia, has a history of more than 3,000 years, extending from the 3^rd millennium BCE to the 13^th century CE. Ḫarrān has long been famous as a religious center of the worship of the moon god Sîn, though he may have originated from the moon god Nanna/Sîn of the Sumerian city Ur. Sîn was politically and religiously developed the most during the Neo-Assyrian Era. Therefore, in order to explore his essence, this paper analyzes the icons and the inscriptions of the Neo-Assyrian steles related to him.</p><p>During the Neo-Assyrian Era, Ḫarrān was in the realm of the Aramaeans. The Assyrian Empire used Sîn of Ḫarrān for its own western expansion policy. Examination of the steles engraved with the crescent moon, the symbol of Sîn of Ḫarrān, reveals that this god was the guarantor of boundaries and had the character of a war god and was incorporated into the Assyrian pantheon. Furthermore, from the distribution of the excavated steles, it is presumed that his original range of influence extended to the whole of northwestern Syria. It is probable that, due to the activities of the Aramaeans and the expansion policy of Assyrian Empire, his influence extended even to present-day Palestine and Jordan.</p><p>In the Aramaean realm of the western territory of the Assyrian Empire, Sîn of Ḫarrān became the guardian god of Assyria’s western expansion policy and possessed overwhelming authority as a guarantor and maintainer of agreements between nations. The steles related to Sîn of Ḫarrān in the Neo-Assyrian Era were the products of this complex view of religion. Eventually, the authority of Sîn of Ḫarrān led to Sîn’s being conceived as the national god by Nabonidus, the last king of the Neo-Babylonian Empire.</p>