Tactics
The extensive road system built by the Inca Empire was meant both to facilitate commerce and to allow rapid deployment of the army (similar to the Roman road system).
A military action would usually be initiated by a military parade to arouse awe in the opposing army. The soldiers would march with their banners and the commander would be carried in his litter carrying the symbol of his command. Should the opposing force still be willing to fight, the general in command (or the Inca himself) would review the troops while musical instruments were played. After this, the commanding officer would rally the troops for the attack. The Sapa Inca himself would rally the troops in larger campaigns, while for smaller rebellions, barbarian invasions, or small campaigns, a general or a prince would be sent as his representative.
The Inca army's military effectiveness was based in two main elements: logistics and discipline. In order to facilitate the movement of their armies, the Inca built a vast road system. Staging areas were set along the roads so the troops and animals could rest, and weapons could be readied. Discipline was very rigid. Soldiers were not allowed to leave the battalion, not even during the approach march. Troops would maintain silence, only breaking it just before attacks by yelling and singing in order to intimidate the opposing force.
Army squads were organized in the following manner: The front lines were initially occupied by slingshot bearers and archers, which would go to the rearguard of the formation after the initial barrages. The lines behind them were occupied by storm-troopers with clubs and axes, then short-spear bearers and closing the formation long-spear bearers (up to 6 meters long).
During a battle on open ground, the Inca army would usually be divided into three groups. The main group would launch a frontal attack against the opposing force while the other two would flank it and circle around behind it to attack from the rear. Before the hand-to-hand combat would start, the Inca army would use ranged weapons (slingshots, arrows and short spears) in order to break the enemy's lines. The army would also feign a retreat, then when the enemy attacked the Incas would counter-attack using a pincer movement.
Most enemies in the region were poorly organized and would perform mass frontal charges after breaking formation. As a matter of fact, the Inca army was so well disciplined that it would not often break formation, being able to effectively repel ambushes in jungle, desert, mountain and swamp terrains.
In the event that the opposing force would take refuge in a fortress, mountain or city, the Inca forces would cut communication and supply lines in order to isolate the enemy and prevent retreat or requests for reinforcements. If negotiations failed, the Inca forces would attempt to storm the fortress and/or starve the opposing force.
Occupied cities and their inhabitants were usually well treated if they surrendered without resistance. However, if the enemy did resist then they could suffer a number of punishments depending on the degree of resistance offered. If a city or tribe surrendered and then rebelled the Inca could even authorize the complete annihilation of the city or ethnic group (as was the case with the Pastos and the Punaeños).
Should retreat be necessary the Inca army would usually march along roads in a disciplined manner along the quickest route available. The army would only rest in fortresses with the objective of re-arming should a counter attack be made. Garrisons would be left in the fortresses that controlled the roads in order to delay a possible advance by the enemy.
A big advantage for the Inca army over its enemies was its numeric superiority. While adversaries were usually warriors from a single tribe (or at most, an alliance of several tribes), the imperial troops were formed of men from all over the empire. Thanks to the large size of the empire, hundreds of thousands of warriors could be mobilized. This wide variety of men would prove both an advantage (numerical superiority and specialized soldiers for different terrain) and a disadvantage (lack of cohesion between army battalions). Both Inca oral histories and Spanish written accounts estimate the Incas could field armies of 100,000 at a time.
The Incas usually sent scouts to watch their enemies, they would also send groups of nobles to negotiate peace treaties and on a number of occasions the servants that they took were spies that tried to bribe enemy officers so that they would betray their kings by retreating during a crucial moment in a battle.
There was a reward system in place for distinguished services. Soldiers displaying bravery beyond expectations were rewarded with medals, metal weapons or other objects and uniforms.
The Incas also built forts (pucará) where they stored arms, food and reserve soldiers. These fortresses also controlled the main communication routes and were constructed in easily defended locations such as in mountains and on the tops of hills or at the side of a river or road.
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