The Building of Concentric Castles
The history of the building of Concentric Castles is fascinating. In just a relatively short period of time a significant number of new Welsh Medieval Castles were built or modernised under the instructions of King Edward I (1272-1307) including Concentric Castles. King Edward employed the services of an architect and master builder called Master James of St George to carry out many of these ambitious plans for a chain of Medieval castles to be built in Wales.
What are Concentric Castles?
The word 'Concentric' is not a commonly used word in this day and age! The definition of the word 'concentric' is "Having a common center" - it doesn't help very much! First there were the wooden 'Motte and Bailey' castles then the Norman's started to build the strong stone Norman Castles, of which the square-shaped Stone Keep was the main feature. King Edward I and his chief architect and builder Master James of St George introduced Concentric Castles. A good description of a Concentric Castle is "a Castle within a Castle". The concentric castle is effectively lots of buildings, walls, towers and gatehouses in one massive castle complex - built within in successive lines of defence! The idea was to make the new Concentric Castles even more secure! Increase the lines of Defence! The Keep or main tower, at the centre of the castle, was the most important building - it housed the Lord, or King of the Castle, his possessions and his family!
The Design of Concentric Castles
The design of Concentric Castles encompassed some, or all, of the following elements:
- A Stronger central Keep or Main Tower
- A Round or Circular Shaped Keep was introduced
- A High wall, complete with towers surrounded the Keep and the Inner Bailey
- At least one lower, outer wall surrounded the Inner High Wall
- Several Outer Walls and Outer Baileys were often added!
- Several Gatehouses were featured
- Moats were added which surrounded the whole Concentric Castle complex
Concentric castles were bigger! The walls were thicker, stronger and higher with turrets! The Inner Walls were higher than Outer walls! Drawbridges were added! The interiors were more comfortable! Concentric Castles were very expensive! Caernarvon Castle cost King Edward I £27,000 - to build this massive Concentric castle today would cost around £40,000,000!
What were Concentric Castles made of?
Concentric Castles were made predominantly of Stone which was generally mined in quarries. The Romans were great builders in Britain and local Roman structures were also pillaged for old Roman bricks. Different types of stone was used:
- Hard Chalk
Lime mortar kept the stones in place. Lime Mortar was made of water, coal, and lime mixed together. Lime stones was first burnt - put into kilns and burnt with coal. It was then mixed with water making Lime Mortar. White plaster was used to cover the walls of castles and also cover the interior walls. The plaster was made from quick lime, sand, water and horse hair. Rubble and Mortar were used for filling inside the walls. Sandstone was used for ornate work around windows. Timber was still used for doors, roofs, frames and scaffolding. Metals, such as lead were used for some roofing elements, door bolts, windows, nails and plumbing. All concentric castles had glass windows! A blob of glass was blown into a cylinder shaped bubble. The cylinder was placed on a cooling table and cut in half. A small piece of glass was produced. The small pieces of glass for the windows were joined together with lead. Concentric castles were made with a variety of materials requiring the skills of many different men. The finished concentric castles would have been a stunning site - especially with the finishing coat of brilliant white plaster.
What were the Strengths and Advantages of Concentric Castles?
The strengths and advantages of concentric castles were as follows:
- Round or Polygonal shaped Keeps or Towers were introduced eliminating the weak corners of the square keeps
- The Square Keeps caused real problems at the corners of the structure:
- It was easy to mine underneath a corner
- The attackers would dig a tunnel underneath one of the corners using timber props (this process was called sapping). The tunnel would be packed with brush wood. The brush wood would be set on fire and the corner would collapse!
- The structure of the castle would be weakened and the weight of the castle would bring the walls caving in and the whole castle would collapse
- Round buildings eliminated defensive blind spots - men could dodge around corners to avoid a direct line of fire which limited attacks from only one direction
- The Concentric Castles were big - allowing a greater number of defendants to be housed in the castle complex
- Moats were added which surrounded the whole Concentric Castle complex. Some were up to 30 feet deep. Moats could be filled with wooden stakes or water. Filling a moat with water would reduce the risk of tunnelling and potential fires
- The various walls were built at different levels - the highest wall being the Inner wall - this allowed the defenders of the concentric castles to have a clear view of any attackers
- The Outer wall, called the Curtain wall, had projecting towers to house defenders. A Curtain wall was built between 6 and 20 feet thick
- Considerable engineering and building skills were put into strengthening and reinforcing the weakest part of the Concentric Castle - The Gateway - the main entrance to the castle
- The addition of a moat led to the introduction of the Drawbridge
- The drawbridge was a wooden bridge which led to the gateway across the moat. The drawbridge was capable of being raised or lowered to either allow or prevent entry into the castle
- The Barbican or 'death trap' was developed as another way to strengthen the main entrance, by adding more defences in front of it.
- The Barbican was an exterior walled passage with multiple gates leading to the main entrance ( the Gatehouse) - the Barbican really was a death trap!
- Defenders would fire arrows from loop holes in the Barbican passage walls
- Only a small number of men were needed to defend this part of the castle
- Holes above the passage ( called Murder Holes ) allowed defenders to drop boiling water, heavy stones or hot sand on the enemy
- The gatehouse was the entrance to the castle containing at least one portcullis
- The gatehouse were built up to three three storeys high
- Ground floor contained the guard rooms
- First floor contained guard quarters and the machinery to operate the portcullis
- Top floor stored weapons and murder holes
- A Portcullis was a heavy grilled door that dropped vertically down to protect the main entrance of the castle
- The Gatehouse might also contain murder holes and arrow loops in the side walls
- The Gatehouse, or main entrance, would be heavily barred - the Chapel was occasionally built in this vicinity - behind the Gatehouse. The enemy would then be seen to fire on the Chapel - God was seen as being on the side of the Defenders of the castle!
- Once the Barbican and the Gatehouse had been breached the enemy would find themselves in an outer bailey and under attack from the bowmen positioned on the walls sheltered by the Crenellations - yet another trap!
- The Crenellations or Battlements provided a fighting platform for the Defenders
- They could fire arrows, or bolts from crossbows, and prevent the enemy from scaling the walls
- The low curtain walls meant that the defenders positioned on the inner walls could monitor the progress of the attackers
- The attackers would then need to attack the Inner Bailey and the Tower or the Keep. The Keep or the Tower was the most strongly defended castle building. Some were as high as 90 feet tall!
The strengths and advantages of concentric castles were numerous!
What were the Weaknesses and Disadvantages of Concentric Castles?
The weaknesses and disadvantages of concentric castles were as follows:
- Concentric Castles were extremely expensive to build
- The loss of a Concentric castle would have been disastrous for the owner
- They required vast man power and labour resources
- A huge variety of skills were required to build Concentric castles
- A Concentric Castle could take several years to complete
- Siege Warfare was applied when trying to take a concentric castle - Castle walls could fall due to bombardment from Siege Engines such as the ballista, the mangonel, and the trebuchet
- Concentric Castles were always built on land containing a well or a spring - so lack of water was not usually a problem
- The Welsh Castles of Edward I were built with direct access to the sea fresh supplies could be delivered to the castle and the defenders could not be starved into submission
- Concentric Castles built inland ran the risk of being starved into submission
Key facts and Information about Concentric Castles
- Heavily Defended
- Round or Polygonal shaped Keeps or Towers
- Various forms of defence - Barbican, Portcullis, Gatehouse, Moat, Crenellations, Murder Holes etc
- Always included access to fresh water within the castle
- Walls were built at different heights and levels
The Concentric Castles
The building of Concentric Castles helped King Edward I to achieve his ambitions and ensured that the Welsh were conquered.