Phalanx System

The Phalanx System was a tactic adopted by the Ancient Greeks between 490-148 BCE. The Hoplite soldiers were formed into a single massed Army shaped like a rectangle.
The Hoplite Phalanx was used with overwhelming success at the Battle of Marathon (490 BCE) and the invasion of Persia (334-330 BCE).

The Phalanx refers to the tactic and was not a fixed number of men.
It tended to be at least 8 rows or more deep with an officer in charge of each row, although at Marathon it was reported to be only 4 rows deep.
Each Hoplite wore his shield on his left arm, relying on his neighbour to protect his right side. This left the right flank inherently vulnerable.
Each rank would lock their shields into a solid line.
The first few rows would then project their spears over the front line of locked shields. This presented a solid wall which was very difficult to break.
The whole Phalanx would then push forward as one unit.
It required flat ground to be successful, which the Greek armies would select in advance.

The Phalanx reached its greatest peak under Alexander the Great who used it to defeat the Persian Empire between 334-330 BCE.
It continued in use until the end of the Macedonian Wars (214-148 BCE), when it was defeated by the Roman Maniple System

Between 550-315 BCE it was adopted by the Roman Kings and the Early Roman Republic.
In 315 BCE it was replaced by the Maniple System.