History of the Peloponnesian War

About this time the Athenians began also to build their long walls down to the sea, both that to Phalerus, and that to Piraeus.

And the Phocians having marched against the Dorians, the mother-country of the Lacedaemonians, [whose towns were] Boeum, and Citinium, and Erineum, and having taken one of these places, the Lacedaemonians under the command of Nicomedes, the son of Cleombrotus, in the stead of Pleistoanax, son of Pausanias, who was yet a minor, went to the aid of the Dorians with fifteen hundred heavy-armed of their own, and ten thousand of the allies; and having compelled the Phocians to restore the town on certain conditions, they proceeded to return back.

Now by sea, if they should wish to cross over the Crissaean Gulf, the Athenians were ready to stop them, having sailed round with a fleet: while the march over Geranea did not appear safe for them as the Athenians were in possession of Megara and Pega. For Geranea was both [naturally] difficult to cross, and was continually guarded by the Athenians : and at that time they knew they were going to stop them that way, as well [as by sea].