Battle of Trans-la-Forêt
Location of Trans-la-Forêt within Brittany region
Date 1 August 939 Location Trans-la-Forêt,Brittany Result Breton victory
Belligerents
Bretons Franks	Vikings
Commanders and leaders
Alan II Judicael Berengar Hugh II of Maine	Unknown

TheBattle of Trans-la-Forêt was fought on 1 August 939 between the occupyingVikings and theBretons, led by a joint army ofAlan II,Hugh II of Maine, andJudicael Berengar.^[1][2][3]

Throughout the early 900's, the states ofBrittany andWest Francia were in a state of flux having both being invaded by the Vikings:

• By 907, a Dane calledHastein conquered an area now calledUpper Brittany, withNantes renamed toNamsborg as their capital.
• In 931, the Vikings assembled an army on the Loire river to attack the Franks. The occupied Bretons seized this opportunity and rebelled. The Vikings appear to have been taken by surprise but a counterattack ensured Brittany was reconquered.
• By 935, the Vikings in Brittany became isolated afterWilliam Longsword of Normandy reconciled with the Franks and exiled Bretons started returning from Anglo-Saxon England. Alan Barbetorte returned to Brittany fromAnglo-Saxon England between 936 and 938, and engaged the Vikings. A Viking leader Incon was slain and Nantes recaptured in 937.
• Receiving support from the Anglo-Saxon KingAthelstan, the Bretons spread their rebellion throughout the peninsula and this brought them into direct confrontation with the Scandinavian colonists.^[4][5]

Through the course of three years, the campaign against the Vikings reached a conclusion at Trans-la-Forêt.

On 1 August 939, a united Breton army led by Alan II, a Breton countJudicael Berengar ofRennes and elements from a Frankish count Hugh II ofMaine decisively attacked and defeated the Viking stronghold, bringing an end to the occupation.

The site of the battlefield is considered to be south ofMont St Michel over the riverCouesnon within a kilometre from Trans-la-Forêt.^[6]

The Breton victory atTrans-la-Forêt freedBrittany of Viking occupation and led to the re-establishment of the Breton State, not as a fully independent Kingdom but as a SovereignDuchy underAlan II, Duke of Brittany, due to a new fealty owed to the Franks for helping remove the Vikings.^[7]

The occupation resulted in Brittany becoming more fortified on the seaward side by returning Breton lords.

Viking piracy continued to affect a previously vibrant maritime trade between the Bretons and their Welsh cousins, isolating the Bretons.

Armorican texts protected by monks for centuries were lost after this period.

The Breton capital was moved from Nantes to inlandRennes as it was regarded as more defensible. This would become a point of discord between the two cities.

• 939
• 930s conflicts
• Battles involving the Vikings
• Battles involving Francia
• Battles involving the Duchy of Brittany
• Military history of Ille-et-Vilaine
• Viking Age in France

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