Megiddo was an ancient fortified city; one of the most famous battlegrounds in the world. Historians believe that more battles were fought at this location than anywhere else on earth: Assyrians, Canaanites, Egyptians, Greeks, Israelites, Persians, Philistines, and Romans. Although Megiddo was not a fortress in the days of World War I, a critical battle enabling the British to wrest control of the Holy Land from the Turks took place here.
'Har' is the Hebrew word for mount or mountain. But in Hebrew the 'h' is silent. Therefore 'Har Megiddo' is pronounced 'Ar Megiddo', arriving at the Greek rendering 'Armageddon'.
Most of us have heard talk about the Battle of Armageddon, being the final battle, but this isn't exactly so. The valley of Megiddo, now known as the valley of Jezreel, will serve as the gathering place; a place where the armies warring against Israel will assemble. Rev 16:16 The final battle will actually take place at Jerusalem and is called the "Battle of That Great Day of God Almighty". Rev 16:14
Note: One of the most significant archaeology finds here at Megiddo was the city's water system. It consists of a vertical shaft 120 feet deep connected by a tunnel 215 feet long to a spring located outside the city walls.
Also, the Valley of Jezreel is a flat plane of land 20 miles long by 14 miles wide, surrounded by mountains.