The surrounding rampart of mountains was broken towards the north-east by an open tract stretching between Hymettus and Pentelicus towards Marathon, and was traversed by the passes of Decelea, Phyle and Daphne on the north and north-west, but the distance between these natural passages and the city was sufficient to obviate the danger of surprise by an invading land force.
The most stirring episode in the history of the Peiraeus is the seizure of Munychia by Thrasybulus and the exiles from Phyle, and the consequent destruction of the "30 tyrants" in 404 B.C. The three chief arsenals of the Peiraeus were named Munychia, Zea and Cantharus, and they contained galley slips for 82, 196 and 94 slips respectively in the 4th century B.C.
Three roads lead to Athens from the Boeotian frontier over the intervening mountain barrier - the easternmost over Parnes, from Delium and Oropus by Decelea, which was the usual route of the invading Lacedaemonians during the Peloponnesian War; the westernmost over Cithaeron, by the pass of Dryoscephalae, or the "Oakheads," leading from Thebes by Plataea to Eleusis, and so to Athens, which we hear of in connexion with the battle of Plataea, and with the escape of the Plataeans at the time of the siege of that city in the Peloponnesian War; the third, midway between the two, by the pass of Phyle, near the summit of which, on a rugged height overlooking the Athenian plain, is the fort occupied by Thrasybulus in the days of the Thirty Tyrants.
The walls and towers also of the city of Eleutherae and the fortress of Phyle are fine specimens of Hellenic fortifications.