Battle of Crogen The Battle of Crogen took place in in the Ceiriog Valley , Wales in 1165 , between the vanguard of the forces of Henry II of England and an alliance of Welsh princes led by Owain Gwynedd . Although outnumbered , the ambush tactics and valour of the Welsh aided them in their defeat of King Henry ' s army . Some sources report that adverse weather conditions also played a major part in Henry ' s defeat . Those weather conditions however were endured by both sides . Background . Henry II , who planned to conquer Wales and so expand the Angevin Empire , raised an army at Oswestry to march to the Berwyn mountains , via the Ceiriog Valley , in the summer of 1165 . Intending to reach the fortresses of Rhuddlan and Basingwerk , Henry II expected resistance and recruited a sizeable force from his kingdoms . Owain , hearing of the invasion , raised an army at Corwen in response , comprising forces from all over Wales . Including his own forces of Gwynedd , led by himself and his brother Cadwaladr , the alliance of princes was made up of men from Deheubarth , under the leadership of Rhys ap Gruffudd , and troops from Powys . The battle . Henry ' s army had the advantage of greater numbers , so Owain ' s tactics were to raid and ambush . He planted skirmisher s in the thick woods overlooking the pass Henry would take . When Henry ' s army advanced into the densely wooded Ceiriog Valley , the Welsh defenders assailed them repeatedly from their positions of cover . Realising the vulnerability of his army , Henry II ordered 2000 woodsmen to clear trees and widen the passage , allowing his forces to move more freely and quickly through the pass . The woodsmen were protected by the best of Henry ' s army and a powerful vanguard of pikemen , but their resistance was only effective for a short period . While the woodsmen cut the trees - his forces were ambushed at the point of Offa ' s Dyke ( which then straddled the valley floor ) at the point where " The Great Oak of the Gate of the Dead " now stands . - a strong force of Owain ' s troops emerged and assaulted Henry ' s vanguard , inflicting severe losses . This engagement was later known as the Battle of Crogen . Henry came within a whisker of losing his life , if not for the brave action of Hugh de St Clare , the Constable of Colchester Castle , who sacrificed his own life when he threw himself in front of a shaft meant for his King . The English forces disengaged and did indeed reach the Berwyn mountains but , hit hard by the Welsh armies , were forced to retreat from Wales altogether when Owain ' s forces succeeded in cutting off their supplies . Aftermath . Estimates of the losses suffered in the battle of Crogen vary , most modern historians consider them to have been relatively light with the English army suffering the bulk of the casualties . The place where this clash occurred is called Adwy ' r Beddau , " the Pass of the Graves " . His attempt at suppression of the Welsh and gaining control of Wales a failure , Henry II ordered Welsh hostages to be brought to him at Shrewsbury , and there oversaw the mutilation of twenty - two prisoners , two of whom were Owain ' s sons . Forced to abandon the conquest of Wales , Henry returned to his court at Anjou , while retaliation for the twenty - two tortured hostages was carried out on Normans throughout the Welsh lands .