The Battle of Ollantaytambo took place in January 1537 between the forces of the Inca emperor Manco Inca and a Spanish expedition led by Hernando Pizarro during the Spanish conquest of Peru. A former ally of the Spaniards, Manco Inca rebelled in May 1536 and laid siege to a Spanish garrison in the city of Cusco. To end the stand-off, the besieged mounted a raid against the emperor headquarters, located in the town of Ollantaytambo. The expedition was commanded by Hernando Pizarro and included 100 Spaniards and some 30,000 Indian auxiliaries against an Inca army of more than 30,000.
There is some controversy over the actual location of the battle, according to John Hemming it took place in the town itself while Jean-Pierre Protzen argues that the nearby plain of Mascabamba is better match for the descriptions of the encounter. In any case, the Inca army managed to hold the Spanish forces from a set of high terraces and flood their position to hinder their cavalry. Unable to advance and severely pressed, the Spaniards withdrew by night to Cusco. Despite this victory, the arrival of Spanish reinforcements to Cusco forced Manco Inca to abandon Ollantaytambo and seek refuge in the heavily forested region of Vilcabamba where an independent Inca state survived until 1572.
In 1531, a group of Spaniards led by Francisco Pizarro landed on the shores of the Inca Empire, thus starting the Spanish conquest of Peru. At that time the empire was emerging from a civil war in which Atahualpa had defeated his brother Huascar to claim the title of Sapa Inca. Atahualpa underestimated the strength of the small force of Spaniards and was captured during an ambush at Cajamarca in November 1532. Pizarro ordered the execution of the Inca in July, 1533, and occupied the Inca capital of Cusco four months later. To replace Atahualpa, Pizarro installed his brother Túpac Huallpa as a puppet ruler but he died shortly afterwards so another brother, Manco Inca, was crowned emperor. During this stage, the only native resistance was carried out by Atahualpa's generals as a sizable part of the empire's population had fought on Huascar's side during the civil war and joined Pizarro against their enemies.
For a while Manco Inca and the conquistadors maintained good relations, together they defeated Atahualpa's generals and reestablished Inca rule on sizable portions of the empire. However, Manco came to realize that real authority rested on Spanish hands when his house was looted with impunity by a Spaniard mob in 1535. Following this episode, the Inca emperor was subject to constant harassment as the Spaniards demanded gold, took away his wives, and even imprisoned him so he fled Cusco to start an uprising. In May 1536, an Inca army laid siege to Cusco, which was garrisoned by a group of Spaniards and native allies. The conquistadors were hard pressed but they managed to resist and counterattack, storming the main Inca stronghold at Sacsayhuaman. Meanwhile, Manco's generals occupied the central highlands of Peru and annihilated several expeditions sent to reinforce Cusco but failed in their attempt to take the recently founded Spanish capital of Lima. As a result of these events, neither side was able to break the deadlock at Cusco for several months so the Spaniards garrison decided to make a direct attack on Manco's headquarters at the town of Ollantaytambo, some 70 kilometers northwest of the city.
Against the Spaniards, Manco Inca had more than 30,000 troops gathered at Ollantaytambo, among them, a large number of recruits from jungle tribes of the Amazon Rainforest. Manco Inca's forces were a militia army made up mostly of conscripted farmers with only rudimentary arms training. This was the regular practice in the Inca empire, where military service formed part of duties of all married men between 25 and 50 years old. In combat, these soldiers were organized by ethnic group and led into battle by their own ethnic leaders, called kurakas. Arms used comprised melee weapon such as maces, clubs and spears as well as ranged weapons such as arrows, javelins, and slings; protective gear included helmets, shields, and quilted cloth armor. With this array of weapons, Inca warriors were at a disadvantage against Spanish soldiers as their wooden clubs and maces with stone or bronze heads were rarely able to kill armored Spaniards. Slings and other missile throwing weapons were somewhat more effective due to their accuracy and the large size of their projectiles. Even so, Inca soldiers were no match for the Spanish cavalry in open terrain so they resorted to fighting on rough terrain and digging pits on open fields to hinder the mobility of horses.
At Ollantaytambo, the Incas relied on fortifications to even their odds against the Spaniards. The main access route to the town runs along a narrow valley formed in the mountains by the Urubamba River, this connects the site with Machu Picchu to the west and with Pisaq and Cusco to the east. After his uprising, Manco Inca fortified the eastern approaches to fend off attacks from the former Inca capital, now occupied by the Spaniards. The first line of defense was a steep bank of terraces at Pachar, near the confluence of the Anta and Urubamba rivers. Behind it, the Incas channeled the Urubamba to make it cross the valley from right to left and back thus forming two more lines backed by the fortifications of Choqana on the left bank and 'Inkapintay on the right bank. Past them, at the plain of Mascabamba, eleven high terraces closed the valley between the mountains and a deep canyon formed by the Urubamba. The only way to continue was through the gate of T'iyupunku, a thick defensive wall with two narrow doorways. In the event of these fortifications being overrun, the Temple Hill, a religious center surrounded by high terraces overlooking Ollantaytambo, provided a last line of defense.
Faced with these constraints, the Spanish expedition had to cross the river several times and fight at each ford against stiff opposition. The bulk of the Inca army confronted the Spaniards from a set of terraces overlooking a plain by the Urubamba River. Several Spanish assaults against the terraces failed against a shower of arrows, slingshots and boulders coming down from the terraces as well as from both flanks. To hinder the efforts of the Spanish cavalry, the most powerful weapon of the Spaniards, the Incas flooded the plain using previously prepared channels; water eventually reached the horses' girths. The defenders then counterattacked; some of them used Spanish weapons captured in previous encounters, such as swords, bucklers, armor and even a horse, ridden by Manco Inca himself. Faced with a severely compromised situation, Hernando Pizarro ordered a retreat; under the cover of darkness the Spanish force fled through the Urubamba valley with the Incas in pursuit and reached Cusco by the next day.
There is some disagreement over the actual location of the battle. According to Canadian explorer John Hemming, Spanish forces occupied a plain between Ollantaytambo and the Urubamba River while the main Inca army was located on a citadel overlooking the town, protected by seventeen terraces. However, Swiss architect Jean-Pierre Protzen argues that the topography of the town and its surrounding area does not match contemporary descriptions of the battle. An anonymous eyewitness account claims that the Inca army occupied a set of eleven terraces, not seventeen; while a chronicle by Pedro Pizarro describes a gate flanked by walls as the only way through the terraces. Protzen thinks that these descriptions allude to a set of eleven terraces that close the plain of Mascabamba, close to Ollantaytambo, which includes the heavily fortified gate of T'iyupunku. At that location, the Spaniards would have been surrounded by the terraces to the front, the Urubamba River to the left and a steep hill called Cerro Pinkulluna to the right, matching the three sides from which they were attacked during the battle. If Protzen's hyphotesis is correct, the river diverted to flood the battlefield was the Urubamba, and not its smaller affluent, the Patakancha, which runs along the town of Ollantaytambo.