本文說明伊庇達姆城邦作為《伯羅奔尼撒戰爭史》首出場角色的用意。伊庇達姆是希臘世界邊陲的蕞爾小邦。修習底德在1.23.3-6 宣稱他為了說明《三十年和約》的爭議才提到伊庇達姆；但他同時認為《三十年和約》爭議並非戰爭根本原因。本文批評1.23.3-6 的說法，說明這個說法簡化歷史，誤導讀者。本文改從《伯羅奔尼撒戰爭史》通篇內容分析伊庇達姆首出場的三層意義。首先，伊庇達姆是引發雅典與斯巴達重要盟邦科林斯衝突的第一起事件。其次，伊庇達姆是預告歷史發展的典型城邦；《伯羅奔尼撒戰爭史》許多重要主題、概念與發展模式都先出現在伊庇達姆。最後，伊庇達姆也是導致雅典與斯巴達戰爭的原因；因為國際交流發達、人們欲望與情緒的惡性循環、也因為神的憤怒，衝突從伊庇達姆這個邊陲小邦蔓延整個東地中海。

This paper examines the historiographic implications of Epidamnus in Thucydides’ History of the Peloponnesian War. Epidamnus, a small city on the northwestern edge of the Greek world, is chosen as the first polis in Thucydides’ war narrative. Thucydides claims that Epidamnus is part of the dispute over the Thirty Years’ Peace; yet, he also resolutely dismisses the significance of the dispute. Thucydides’ explanation is oversimplifying and confusing. Taking into account of the entire war narrative of the History, we find three reasons for Epidamnus as the first polis of the war narrative. First, the dispute over Epidamnus leads to the first military conflict between Athens and Corinth, an important ally of Sparta. Second, Epidamnus is a typical polis; it introduces major issues and historical patterns in the History. Third, Epidamnus is also a cause of the war. The international network, human desires and passions, and the divine fury all bring the local conflict of Epidamnus into the Greek world and beyond.