The Odrysian kingdom was founded by king Teres I, exploiting the collapse of the Persian presence in Europe due to failed invasion of Greece in 480-79. Teres and his son Sitalces pursued a policy of expansion, making the kingdom one of the most powerful of its time. Throughout much of its early history it remained an ally of Athens and even joined the Peloponnesian War on its side. By 400 the state showed first signs of fatigue, although the skilled Cotys I initiated a brief renaissance that lasted until his murder in 360.