Asea is located in the heart of the Peloponnese. The Asea valley was inhabited, first in the Middle/Upper Paleolithic period (ca. 40.000 B.P) by people making their living from hunting and fishing. During most of the Neolithic period and the Bronze Age there were several villages in the valley, of which the most important one was located on the Asea Paleokastro hill.
Aphidna was in Classical times one of the Attic demes and an important fort protecting the northern Attic border. The fortress is situated on the acropolis of Kotroni on the northwestern edge of the Marathon Lake.