The phalanx formation is an Ancient Greek term for a block-like infantry formation. The Greek hoplites (heavy infantry) were armed with spears, swords, or similar weapons. The mass of infantry marched forward as one entity against opponents. The system was used by city states, who often fought each other. Cavalry were rare, partly because horses were a scarce resource, and partly because the lack of space on valley floors in the Peloponnese left little room for cavalry manoeuvres. Later, the Macedonian phalanx was always supported by cavalry in the conquests of Alexander the Great.