The battle of Tinchebray (or Tinchebrai) was fought September 28, 1106, in the town of Tinchebray, 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 until his death. England and Normandy remained under a single ruler for some years thereafter.
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 is usual for the period). These were commanded by Ranulf of Bayeux, Robert de Beaumont, Count of Meulan, and William de Warenne. In addition he had a reserve, commanded by Helias, Count of Maine, hidden out of sight. Also on Henry's side were Alan, 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.
The battle itself only lasted an hour. 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 spent the rest of their lives in captivity.