The phalanx (pl.: phalanxes or phalanges) was a rectangular mass military formation, usually composed entirely of heavy infantry armed with spears, pikes, sarissas, or similar polearms tightly packed together. The term is used today to describe the use of this formation in ancient Greek warfare, but ancient Greek writers used it more broadly to describe any massed infantry formation regardless of its equipment. In Greek texts, the phalanx may be deployed for battle, on the march, or even camped, thus describing the mass of infantry or cavalry that would deploy in line during battle. They marched forward as one entity.
The term itself, as used today, does not refer to a distinctive military unit or division (e.g., the Roman legion or the contemporary Western-type battalion), but to the type of formation of an army's troops. Therefore, this term does not indicate a standard combat strength or composition but includes the total number of infantry, which is deployed in a single formation known as a "phalanx".