Battle of Aljubarrota The Battle of Aljubarrota ( ) was a battle fought between the Kingdom of Portugal and the Crown of Castile on 14 August 1385 . Forces commanded by King John I of Portugal and his general Nuno Álvares Pereira , with the support of English allies , opposed the army of King John I of Castile with its Aragonese , Italian and French allies at São Jorge place , between the towns of Leiria and Alcobaça , in central Portugal . The result was a decisive victory for the Portuguese , ruling out Castilian ambitions to the Portuguese throne , ending the 1383 – 85 Crisis and assuring John as King of Portugal . Portuguese independence was confirmed and a new dynasty , the House of Aviz , was established . Scattered border confrontations with Castilian troops would persist until the death of John I of Castile in 1390 , but these posed no real threat to the new dynasty . To celebrate his victory and acknowledge divine help , John I of Portugal ordered the construction of the monastery of " Santa Maria da Vitória na Batalha " and the founding of the town of Batalha ( Portuguese for " battle " , ) . The king , his wife Philippa of Lancaster , and several of his sons are buried in this monastery , today a UNESCO World Heritage Site . Prelude . The end of the 14th century in Europe was a time of revolution and crisis , with the Hundred Years ' War between the English and the French for Western France , the Black Death decimating the continent , and famine afflicting the poor . Portugal was no exception . In October 1383 , King Ferdinand I of Portugal died with no son to inherit the crown . The only child of his marriage with Leonor Telles de Meneses was a girl , Princess Beatrice of Portugal . In April of that same year the King signed the Treaty of Salvaterra de Magos with King Juan I of Castile . The treaty determined that Princess Beatrice was to marry Juan I , king of Castile , and the Crown of Portugal would belong to the descendants of this union . This situation left the majority of the Portuguese discontent , and the Portuguese nobility was unwilling to support the claim of the princess because that could mean the incorporation of Portugal to Castile ; also the powerful merchants of the capital , Lisbon , were enraged from being excluded from the negotiations . Without an undisputed option , Portugal remained without king from 1383 – 85 , in an interregnum known as the 1383 – 85 Crisis . The first clear act of hostility was taken in December 1383 by the faction of John ( João ) , the Grand Master of the Aviz Order ( and a natural son of Peter I of Portugal ) , with the murder of Count Andeiro . This prompted the Lisbon merchants to name him " rector and defender of the realm " . However , the Castilian king would not relinquish his and his wife ' s claims to the throne . In an effort to normalize the situation and secure the crown for him or Beatrice , he forced Leonor to abdicate from the regency . In April 1384 , in Alentejo , a punitive expedition was promptly defeated by Nuno Álvares Pereira , leading a much smaller Portuguese army at the Battle of Atoleiros . This marked the first use of English defensive tactics on the Iberian peninsula , reportedly without any casualties to the Portuguese . A larger second expedition led by the Castilian king himself reached and besieged Lisbon for four months before being forced to retreat by a shortage of food supplies due to harassment from Nuno Álvares Pereira , and the bubonic plague . In order to secure his claim , John of Aviz engaged in politics and intense diplomatic negotiations with both the Holy See and England . On 6 April 1385 , ( the anniversary of the " miraculous " battle of Atoleiros , a fortuitous date ) , the council of the kingdom ( " cortes " in Portuguese ) assembled in Coimbra and declared him King John I of Portugal . After his accession to the throne , John I of Portugal proceeded to annex the cities in whose military commanders supported Princess Beatrice and her husband ' s claims , namely Caminha , Braga and Guimarães among others . Enraged by this " rebellion " , Juan I ordered a host of 31 , 000 men to engage in a two - pronged invasion in May . The smaller Northern force sacked and burnt populations along the border , a common practice at the time and similar to what the English were doing in Scotland , before being defeated by local Portuguese nobles in the battle of Trancoso , on the first week of June . On the news of the invasion by the Castilians , John I of Portugal ' s army met with Nuno Álvares Pereira , the Constable of Portugal , in the town of Tomar . There they decided to face the Castilians before they could get close to Lisbon and lay siege to it again . English allies arrived on Easter of 1385 , consisting of a company of about 100 English longbowmen , veterans from the Hundred Years ' War , sent to honor the Anglo - Portuguese Treaty of 1373 ( presently the oldest active treaty in the world ) . The Portuguese set out to intercept the invading army near the town of Leiria . Nuno Álvares Pereira took the task of choosing the ground for the battle . The chosen location was São Jorge near Aljubarrota , in a small flattened hill surrounded by creeks , with the very small settlement of Chão da Feira ( Fair ' s Ground ) at its widest point , still present today . Portuguese dispositions . At around 10 o ' clock in the morning of 14 August , the army of John I took its position at the north side of this hill , facing the road where the Castilians would soon appear . As in other defensive battles of the 14th century ( Crécy or Poitiers , for example ) , the dispositions were the following : dismounted cavalry and infantry in the centre with archers occupying the flanks . Notably , on the vanguard ' s left wing ( later covering the left flank ) , a company composed by some two hundred unmarried young nobles is remembered to history as the " Ala dos Namorados " ( Sweethearts ' Flank ) ; the right wing , also two hundred strong , known as " Ala de Madressilva " or Honeysuckle Flank , didn ' t achieve the same heroic fame . On either side , the army was protected by natural obstacles ( in this case , creeks and steep slopes ) . In the rear , reinforcements were at hand , commanded by John I of Portugal himself . In this topographically high position , the Portuguese could observe the enemy ' s arrival and were protected by a steep slope in their front . The rear of the Portuguese position , which was in fact its front in the final battle , was at the top of a narrow slope , which came up to a small village , and was further constricted by a complex series of interlocking trenches and caltrops designed to surprise and trap the enemy cavalry . This trenching tactic was developed around this time and used extensively by both the English in France and the Portuguese in the rare set - piece battles of the Crisis of the Succession . Castile arrives . The Castilian vanguard arrived at lunch time from the north . Seeing the strongly defensive position occupied by the Portuguese , John of Castile made the wise decision to avoid combat on John of Portugal ' s terms . Slowly , due to the numbers of his army ( about 31 , 000 men ) , the Castilian army started to contour the hill where the Portuguese were located . John of Castile ' s scouts had noticed that the South side of the hill had a gentler slope and it was there that the Castilian king wanted to attack . In response of this movement , the Portuguese army inverted its dispositions and headed to the South slope of the hill . Since they were fewer than the enemy and had less ground to cover , they attained their final position very early in the afternoon . To calm the soldiers ' nervousness and to improve his army ' s defensive position , general Nuno Álvares Pereira ordered the construction of a system of ditches , pitches and caltrop s . This application of typical English tactical procedures had also been used by the Portuguese on the previous battle of Atoleiros and was especially effective against cavalry ( the speciality of both the Castilian and the French armies ) . Around six o ' clock in the afternoon the Castilian army was ready for battle . According to John of Castile ' s own words , in his report of the battle , his soldiers were by then very tired from the march that started early in the morning under a blazing August sun . There was no time to halt now , and the battle would soon begin . Battle . The initiative of starting the battle was with the Castilian side . The French allied heavy cavalry charged , as they were accustomed to do , in full strength , in order to disrupt order in the enemy lines . Even before they could get into contact with the Portuguese infantry , however , they were already disorganized . Just as at Crécy , the defending archers and crossbowmen , along with the ditches and pits , did most of the work . The losses of the cavalry were heavy and the effect of its attack completely null . Support from the Castilian rear was late to come and the knights that did not perish in the combat were made prisoners and sent to the Portuguese rear . At this point the main Castilian force entered the battle . Their line was enormous , due to the great number of soldiers . In order to get to the Portuguese line , the Castilians became disorganized , squeezing into the space between the two creeks that protected the flanks ; it was not an auspicious start . At this time , the Portuguese reorganized . The vanguard of Nuno Álvares Pereira divided into two sectors . Since the worst was still to come , John of Portugal ordered the archers and crossbowmen to retire , while his rear troops advanced through the space opened between the vanguards . With all his troops needed at the front , there were no men available to guard the knight prisoners ; John of Portugal ordered them to be killed on the spot and proceeded to deal with the approaching Castilians . Advancing uphill with the sun on their backs , squashed between the funnelling Portuguese defensive works and their own advancing rear , and under a heavy rain of English longbowmen ' s arrows shot from behind the Portuguese line and crossbow quarrels from behind both the Sweethearts ' and the Honeysuckle wings on their flanks , the Castilians did their best to win the day . The Castilian knights on the main body were forced to dismount and break in half their unwieldy four metre - long lances in order to join the constricted melèe alongside their infantry . At this stage of the battle , both sides sustained heavy losses , especially on the " Ala dos Namorados " where the Portuguese students became renowned for holding off the heavily armoured knights of the Castilian wings who , still on horseback , attempted to flank the Portuguese lines . A similar attack was more successful on the right " Honeysuckle " flank , though only briefly and late in the fight . By sunset , only one hour after the battle began , the Castilian position was indefensible and the situation quite desperate . When the Castilian royal standard - bearer fell , the already demoralized troops on the rear thought their King was dead and started to flee in panic ; in a matter of moments this became a general rout where Juan of Castile himself had to run at full speed to save his life , leaving behind not only common soldiers but also many still dismounted noblemen . The Portuguese pursued them down the hill and , with the battle won , killed many more while there was still light enough to see the enemy . Aftermath . During the night and throughout the next day , as many as 5000 more Castilians were killed by the neighbouring towns ' villagers ; according to Portuguese tradition surrounding the battle , there was a woman called Brites de Almeida , the " Padeira of Aljubarrota " ( the baker - woman of Aljubarrota ) , said to be very tall , strong , and to possess six fingers on each hand , who ambushed and killed by herself eight Castilian soldiers as they were hiding in her bakery trying to save their lives after the battle in the town of Aljubarrota itself . This story in particular is clouded in legend and hearsay . But the popular intervention in the massacre of Castilian troops after the battle is , nevertheless , historical and typical of battles in this period when there was no mercy toward the defeated enemy . In the morning of the following day , the true dimension of the battle was revealed : in the field , the bodies of Castilians were enough to dam the creeks surrounding the small hill . In face of this , the Portuguese King offered the enemy survivors an amnesty and free transit home ; an official mourning was decreed in Castile that would last until the Christmas of 1387 . The French cavalry contingent suffered yet another defeat ( after Crécy and Poitiers ) by English defensive tactics , even though they finally defeated the English and unified their country after the 100 years war . The battle of Agincourt decades later would show that they still had a lesson to learn . In October 1385 , Nuno Álvares Pereira led a pre - emptive attack against Mérida , in Castilian territory , defeating an even larger Castilian army than at Aljubarrota in the battle of Valverde , in Valverde de Mérida . Scattered border skirmishes with Castilian troops would persist for five years more until the death of John I of Castile in 1390 , but posed no real threat to the Portuguese crown ; recognition from Castile would arrive only in 1411 with the signature of the Treaty of Ayllón ( Segovia ) . As stated above this victory assured that John of Aviz was the uncontested King of Portugal and the House of Aviz ascended to the crown of Portugal . In 1386 , the closeness of relations between Portugal and England resulted in a permanent military alliance with the Treaty of Windsor , the eldest still active in existence . His marriage to Philippa of Lancaster in 1387 initiated the Portuguese second dynasty , and their children went on to make historically significant contributions in their own right . Duarte , or Edward of Portugal , became the eleventh King of Portugal , and was known as " The Philosopher " and " The Eloquent " . Henrique , or Henry the Navigator , sponsored expeditions to Africa .