Battle of Jengland The Battle of Jengland ( also called Jengland - Beslé , Beslé , or Grand Fougeray ) took place on 22 August 851 , between the Frankish army of Charles the Bald and the Breton army of Erispoe , Duke of Brittany . The Bretons were victorious , leading to the signing of the Treaty of Angers in September 851 which secured Breton independence . Background . In 845 , Nominoë , Duke of Brittany , had defeated Charles the Bald at the Battle of Ballon . A truce had followed , but in 849 Nominoë resumed his offensive against the Franks . He sought to establish full personal control over his duchy and extend its territory . In 851 , Frankish garrisons left in the previous year in Rennes and Nantes capitulated to Nominoë , who raided eastwards , ravaging Le Mans . Nominoë then decided to advance to Chartres , but died suddenly , near Vendôme . His successor , his son Erispoe , took command of the Breton force and continued its offensive in alliance with Lambert II of Nantes , a renegade Frank dispossessed by Charles the Bald . Faced with the threat , Charles sought the support of his brother Louis the German , obtaining a contingent of Saxons to increase the size of his force . He marched to confront Erispoe , who retreated back to the borders of Brittany . Both leaders probably led smallish armies , with Charles commanding around 4 , 000 troops and Erispoe around 1 , 000 . The battle . In August 851 , Charles left Maine to enter Brittany by the Roman road from Nantes to Corseul . The king arranged his troops in two lines : at the rear were the Franks ; in front were Saxon mercenaries whose role was to break the assault of the Breton cavalry , which was known for its mobility and tenacity . In the initial engagement , a javelin assault forced Saxons to retreat behind the more heavily armoured Frankish line . The Franks were taken by surprise . Rather than engage in a melée , the Bretons harassed the heavily armed Franks from a distance , in a manner comparable to Parthian tactics , but with javelins rather than archers . They alternated furious charges , feints and sudden withdrawals , drawing out the Franks and encircling over - extended groups . After two days of this sort of fighting , Frankish losses in men and horses were mounting to catastrophic levels , while the Bretons suffered few casualties . With his force disintegrating , Charles withdrew from the field during the night . When his disappearance was noticed the following morning , panic seized the Frankish soldiers . The Bretons quickly raided the camp , taking booty and weapons and killing as many fugitives as they could . Treaty of Angers . The battle redefined relations between Franks and Bretons . Charles the Bald agreed to meet Erispoe in Angers , on the outskirts of the now - extended territory of Brittany . In September 851 Erispoe submitted to Charles as Emperor , while receiving the title of king in return . According to the Annals of Saint - Bertin " Erispoe , son of Nominoë from Charles , in the City of Angers submitted and received a gift of symbols of the monarchy that came from his father , adding also Rennais , Nantais and Retz . " By the treaty , Erispoe remained in principle subject to Charles the Bald , but could now also see himself Charles ' s equal , able to use the title of " rex " . Charles recognized the authority of Breton rulers over the areas around Rennes , Nantes and Pays de Retz , which had previously formed the Frankish " Breton March " , a border zone . Erispoe , at the same time , absorbed a non - Breton speaking population of Gallo - Roman and Romano - Frankish peoples . The Treaty of Angers demarcated the borders of the medieval Duchy of Brittany and the later French province of Brittany . It also marked a turning point in relations between the Western Franks and Brittany . Later Breton dukes were able to extend their territory further , but were unable to hold it for long . The Treaty of Angers essentially defined the limits of historic Brittany . The peace created by the regularisation of Franco - Breton relations also gave the Bretons the stability to fend off later Viking attacks .