The Battle of Tinchebray (alternate spellings Tinchebrai or Tenchebrai) was fought 28 September 1106, in the town of Tinchebray (in today's Orne département of France (48 45' 54.98"N, 0 43' 40.18"W)), Normandy, between an invading force led by Henry I of England, and his older brother Robert Curthose, the Duke of Normandy. Henry's knights won a decisive victory, capturing Robert and imprisoning him in England and then Wales until Robert's death in Cardiff Castle. England and Normandy remained under a single ruler until 1204.
The previous year Henry had invaded Normandy, taking Bayeux and Caen. He was forced to break off his campaign due to political problems arising from the Investiture Controversy. With these settled, he returned to Normandy in the summer of 1106. After quickly taking the fortified abbey of Saint-Pierre sur Dives (near Falaise), Henry turned south and besieged the castle of Tinchebray, on a hill above the town. Tinchebray is on the border of the county of Mortain, in the southwest of Normandy, and was held by the count, who was one of the few important Norman barons still loyal to Robert.
Robert brought up his forces to break the siege, and, after some unsuccessful negotiations, battle was inevitable.
Henry's army was organized into three groups (as was usual for the period). These were commanded by Ranulf of Bayeux, Robert de Beaumont, 1st Earl of Leicester, and William de Warenne, 2nd Earl of Surrey. In addition he had a reserve, commanded by Elias I of Maine, out of sight on the flank. Also on Henry's side were Alan IV, Duke of Brittany, William, Count of Evreux, Ralph of Tosny, Robert of Montfort, and Robert of Grandmesil. On Robert Curthose's side were William, Count of Mortain, and Robert of Bellême, 3rd Earl of Shrewsbury.
The battle itself only lasted an hour. Notably, Henry ordered much of his force of knights to dismount, as he did himself: unusually for Norman battle tactics, infantry played a decisive role. The count charged the front line, comprising troops of Bayeux, Avranches and the Cotentin. The intervention of Henry's reserve proved decisive. Most of Robert's army was captured or killed. Besides Robert himself, those captured include Edgar Atheling (uncle of Henry's wife), and William, count of Mortain.
Most of the prisoners were released, but Robert Curthose and William of Mortain were to spend the rest of their lives in captivity.