William Marshal was the fourth son of John FitzGilbert, Marshal at the Court of King Stephen. 
John FitzGilbert was a ruthless warrior who held castles in Wiltshire at Marlborough and Ludgershall at a time while England was embroiled in civil war and anarchy. Side changing was common and John FitzGilbert forsook Stephen and sided with Matilda. 
During the fluctuating fortunes of both sides of the conflict, FitzGilbert gave his five year old fourth son, William, as a hostage to Stephen in pledge of his good behavior during a brokered truce. FitzGilbert broke the truce, using the peaceable time to resupply and strengthen his castle at Newbury. 
This resulted in him being besieged in 1152 by Stephen who threatened to catapult his hostage, FitzGilbert’s son, over the castle walls. The ruthless FitzGilbert famously declared that he had ‘the anvils and the hammer to forge still better sons’. Stephen forbore to catapult young William or to fulfil his subsequent threat to hang the child, and so William survived to become ‘The Greatest Knight who ever lived’!
