Athens Long Walls
You can read about Athens Walls in general here.
Long Walls were built actually after Athens was absolutely destroyed after Persian invasion of 480 BC and its defense line and strategy was redesigned. The third and best
fortification line connected Athens to Piraeus -the famous Themistocles’ wall, built in 479 BC. It was the basis of defence that gave Athens the upper hand to control the ancient world’s trade. It was 6500 metres in perimeter and had 13 gates. The Walls were finished by Cimon in 456 BC and completed by Pericles ten years later.
Most of the Long Walls’ parts were demolished after Athens defeat in Peloponnesian War in 404, but Athens regained its power very soon and in 395-394 BC a part of the Wall was rebuilt again. Athens was rebuilding its empire, but Macedonians stopped it. In order to defense them, Athenians built Proteichisma in 338 BC, so the Nymph, Mouson and Pnyx hills were protected by a defense wall. After Alexander’s Macedonia the Long Walls had no use. Diateichisma was built in 280 BC.
Athens Walls were in not that bad condition, but were destroyed during Roman Sulla raid to Athens (87-86 BC). It was the time that Athens lost its ancient glory, and the time that was becoming a more religious center started. Athens was already a Roman province.