Near the coastal village Porto Germeno in West Attica, 450m from the sea lies the ancient fortress of Aigosthena, an ancient fortress that remained on use in the early Byzantine period and maybe later. It is rather in the best condition among the ancient forts that are preserved in Greece.
In the classical period Aigosthena belonged to Megara. The fortress was built sometime around the early 4th to the early 3rd century BC, most probably in 343 BC when the Athenians were helping the city-state of Megara to confront the threat of Thiva. For this reason, the fort was manned by a guard of Athenians.