Later these communities were organized into poleis or city-states. The mountains prevented large-scale farming and impelled the Greeks to look beyond their borders to new lands where fertile soil was more abundant. Natural resources of gold and silver were available in the mountains of Thrace in northern Greece and on the island of Siphnos, while silver was mined from Laurion in Attica. Supplies of iron ores were also available on the mainland and in the Aegean islands. Summers are generally hot and dry.
Winters are moderate and rainy in coastal regions and cold and snowy in mountainous areas.