Stone or square keep castles were first built in Medieval England by William the Conqueror. Stone keep castles were the natural extension of motte and bailey castles. Motte and bailey castles were only temporary features (though many mottes exist to the day) while stone keep castles were built to last.
After the “Harrying of the North”, William decided to show no mercy to the English. Stone keep castles were the ultimate sign of his power over the English. The most famous of these castles were in London (the White Tower at the Tower of London) and Rochester Castle in Kent.
The use of stone allowed stone keeps to be built in an entirely different way from motte and bailey castles. Stone was a strong building material that allowed the builder to build up. Motte and bailey castles were built out of weaker wood and builders were limited to the size and height they could go to.
However, with a strong foundation, stone keep castles could be built high. This gave them the great advantage of visibility – allowing the defenders to see if an enemy was coming when they were still a distance away – thus allowing the castle to get its defences ready. Rochester Castle has views across the Medway estuary, so any attack by river would have been easy to spot.
Stone keeps had other defensive mechanisms. Motte and bailey castles were open to being set on fire. This was possible with stone keeps but it was much more difficult to set a stone keep alight. Whereas motte and bailey castles were surrounded by a wooden fence, the stone keeps could rely on outer walls made of stone (curtain walls). William’s stone keeps also had their ‘front’ door on the first floor. Wooden steps led up to it. If it was attacked, these steps would be knocked down. Those inside the keep would be isolated but those seeking to attack it, would have to get inside it somehow.
The most famous stone keep castle must be the White Tower at the Tower of London.
William had decided to make London his capital. To defend his supply ships coming up the River Thames, he built the imposing White Tower that was meant to intimidate those who lived in London. The White Tower was built just inside the city walls built by the Romans. William entrusted the early building work to a monk called Gundulf, who later became Bishop of Rochester. The White Tower has four irregular sides - though they look square, they are all of a different length. Three of the corners are also not at right-angles. This, however, was simply a reflection on the primitive equipment the Normans had to use as opposed to any lack in building skills.
To the people of London, the completed building must have represented an awesome sight. The White Tower was, at 90 feet tall, the highest building in London. The thickness of the walls varies from 15 feet thick at the base to 11 feet thick in the upper storey. The White Tower was massively strong - it was never taken in combat and only fell to an 'enemy' in 1381 during the Peasants' Revolt when sympathetic guards let in the rebels. In military terms, the castle was never taken, and it is difficult to see how an enemy could have taken the White Tower with the weapons that existed in Medieval England.
The White Tower was built out of stone brought from Caen in northern France. William did not 'trust' Saxon stone and brought in stone from his own lands. He also used architects and builders he could trust while the heavy unskilled work was done by the English. Caen stone was a creamy yellow and gave the White Tower its nickname. However, in 1241, Henry III had the whole of the outside whitewashed so that it definitely became the White Tower!
William ensured that the White Tower had everything he needed kept within it. There was a well for fresh water, dormitories for sleeping, royal chambers for himself, a private chapel, huge open fires and guarderobes (toilets), kitchens etc. Should the keep ever be put in a position whereby it was isolated, William believed that it and he were in a position to defend themselves.
Rochester Castle is even higher than the White Tower standing at 113 feet - the highest stone keep castle in England. The walls of this castle are between 11 and 13 feet thick. Gundulf was again the chief architect here and he built the castle along the same geographic lines as a Roman fort that had been built at Rochester. The castle at Rochester was originally built for the Archbishop of Canterbury.
Square keep castles cost a fortune to build. A king in Medieval England, on average, had about £10,000 to spend each year. The castle at Dover cost £4000. Rochester Castle cost about £3000 - i.e. a third of the king's annual income each year. This was at a time when a skilled labourer earned just 2 pence a day.
Rochester Castle was the scene for a noble rebellion against the rule of King John in 1215.