In 432 King Perdiccas II of Macedon encouraged several nearby coastal towns to disband and remove their population to Olynthus, preparatory to a revolt to be led by Potidaea against Athens (Thuc. 1.58). This synoecism (συνοικισμός) was effected, though against Perdiccas's wishes the contributing cities were preserved. This increase in population led to the settlement of the North Hill, which was developed on a Hippodamian grid plan. In 423 Olynthus became the head of a formal Chalkidian League, occasioned by the synoecism or by the beginning of the Peloponnesian War and fear of Athenian attack. During the Peloponnesian war it formed a base for Brasidas in his expedition of 424 and refuge for the citizens of Mende and Poteidaea that had rebelled against the Athenians (Thu. ii, 70).