The Municipality of Marathon belongs to the Peripheral Unity of Eastern Attica and its present form is due to the consolidation of the former municipalities of Nea Makri and Marathon and the communities of Grammatiko and Barnabas, according to the Kallikratis Program.
The Municipality has an area of ​​226,55 km2 and a population of 33,423 inhabitants, based on the latest census of 2011.
The seat of the Municipality of Marathon was the town of Marathon.
Marathon was an ancient city of Attica, built in a plain. The area remained in history due to the great battle that took place there in 490 BC between the Athenians and the Persians. According to tradition, the city and the surrounding area have been named after a local hero, fennel plant that thrived in these places. Later the settlements of Marathon were united in a federation of four municipalities called Tetrapolis of Attica. The rest of the cities were Provalinthos, Oinoi and Trikorithos, but Marathon was the most important and for this it became a municipality of Athens.
Modern Marathon has a fertile plain that helps crops. In the area there is also the artificial lake of Marathon, built in 1926-31 with a capacity of 42,000,000 cubic meters. and for years it has been the exclusive source of water in Athens. Its importance today is great.