The Euboean League was an ancient Greek alliance formed by the island of Euboea and its neighboring territories. Established in the 5th century BCE, it aimed to promote mutual defense and economic cooperation among its members. The league played a significant role during the conflicts of the time, particularly during the Peloponnesian War. The league's most notable city was Chalcis, which served as a central hub for political and military activities. Over time, the Euboean League faced challenges from larger powers, including the Athenian Empire and the Macedonian Kingdom, leading to its eventual decline in influence and autonomy.