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.

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.^[1]

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.

In August, 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.^[2]

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.^[1]

The battle redefined relations between the Franks and Bretons. Charles the Bald agreed to meet Erispoe in Angers, on the outskirts of the now-extended territory of Brittany.