How to build a medieval castle: 9 top tips

Castles were commonly erected on naturally prominent sites, usually commanding a landscape or a communication link, such as a ford, bridge or pass.

It is rare to have a medieval account of the circumstances behind the choice of a castle site but they do exist. On 30 September 1223, the 15-year-old king Henry III arrived in Montgomery with an army. The king, having campaigned successfully against the Welsh prince Llywelyn ab Iorwerth, was intent on creating a new castle in the area to secure the border of his realm. Carpenters in England had been charged with preparing timber for the new fortifications a month previously, but the king’s advisers determined where the castle should be sited.

After surveying the area carefully they chose a spot on the very edge of a promontory above the valley of the river Severn. It was, in the words of the chronicler Roger of Wendover, a position “that seemed untakeable to everyone”. He also observed that the castle was “for the security of the region on account of the frequent attacks of the Welsh”.

Top tip: Identify the places where the topography dominates transport routes: these are natural sites for castles. Bear in mind that the castle’s design will be shaped by the building’s position. A castle on a high outcrop will, for example, have dry moats.

• England's 8 most amazing castles

Agree on a workable design

A master mason who can draw plans is a must – while an engineer who knows all about weapons is useful too

Experienced soldiers may have had ideas of their own about the design of their castle, in terms of the form of the buildings and their arrangement. But it’s unlikely they would have had any specialist knowledge in design or building.

What was needed to realise a vision was a master mason – an experienced builder whose distinguishing skill was the ability to draw. With an understanding of practical geometry he used the simple tools of a measuring rod, set-square and compass to create architectural designs. Master masons would present a drawn proposal for the castle for approval and when building commenced would oversee its construction.

When Edward II began building a great residential tower at Knaresborough Castle in Yorkshire for his favourite, Piers Gaveston, in 1307, he not only approved the design, created by the London master mason Hugh of Titchmarsh – presumably expressed as a drawing – but also demanded from him regular reports on the progress of the work. From the mid-16th century, a new group of professionals, termed engineers, increasingly came to dominate the design and construction of fortifications. They had a technical understanding of the use and power of cannon, both in protecting and reducing castle defences.

Top tip: Plan arrow slits carefully for a wide field of fire. Shape according to the weapons you use: longbow men need large splays (the oblique angles in the side of an opening in a wall); crossbow men less so.

Source a large, and skilled, workforce

You’ll need thousands of men – not necessarily all there by choice

The labour required to build a great castle was vast. We have no documentary evidence for the numbers involved in the first great round of castle-building in England, after 1066, but the scale of many castles of this period makes it clear why some chronicles speak of the English population as being oppressed by the castle construction of their Norman conquerors.In the later Middle Ages, however, surviving building accounts offer detailed information.

During his first invasion of Wales, in 1277, Edward I began building a castle at Flint, north-east Wales. This was erected at speed, using the massive resources of the crown. Within a month of starting work, in August that year, 2,300 men were employed on site, including 1,270 diggers, 320 woodmen, 330 carpenters, 200 masons, 12 smiths and 10 charcoal burners. All these men were pressed into service from across the realm and accompanied into Wales with guards to prevent desertion.

In every period, foreign specialists were employed where necessary, often in senior roles. The millions of bricks needed to remodel Tattershall Castle, Lincolnshire during the 1440s, for example, were supplied by a certain Baldwin the ‘Docheman’ or Dutchman, evidently an immigrant.

Top tip: Depending on the size of your workforce and the distance it has travelled, it may be necessary to provide accommodation on site.

Secure the building site

A work-in-progress in hostile territory is extremely vulnerable to attack from the enemy before it is ready

In order to build a castle in hostile territory it was essential to protect the site from attack. One way of doing this was to enclose the construction area within a timber fortification or low stone wall. Such medieval defences have sometimes been preserved in the completed building as an outer apron wall, as can be seen at Beaumaris, Anglesey, begun in 1295.

No less important was the need to secure communications with the outside world for the delivery of building materials and supplies. In 1277, for example, Edward I canalised the river Clwyd at vast expense from the sea to his new castle at Rhuddlan. Here, the apron wall built to protect the building site extended down to the quay on the banks of the river.

There might also have been concerns for security during major alterations to an existing castle. When Henry II remodelled Dover Castle, Kent in the 1180s, his building operation appears to have been carefully staggered so that the fortifications were continuously defensible throughout the construction process.

According to surviving royal accounts, work to the inner bailey wall was only begun when the great tower or keep was sufficiently complete to be garrisoned.

Top tip: Castle-building materials are big and bulky. If at all possible, try and move them by water, even if you have to build a dock or canal to do so.

• 10 things you might not know about the Middle Ages

Landscape the area

Building a castle might involve moving a massive amount of earth, at great cost

It is often forgotten that castle fortifications were as much works of landscaping as of architecture. The resources involved in moving earth without pieces of machinery was necessarily enormous. Even after long neglect, the scale of Norman earthworks in particular can be extraordinary. It has been estimated, for example, that the vast artificial mound, termed a motte, erected in around 1100 at Pleshey Castle, Essex, required 24,000 days of labour to raise.

Some aspects of landscaping were also highly skilled, notably the creation of moats filled with water. When Edward I remodelled the Tower of London in the 1270s, he employed a foreign specialist, Walter of Flanders, to create a huge new tidal moat around the site. The ditching work that Walter supervised cost more than £4,000 to complete, an enormous sum that was nearly a quarter of the cost of the entire project.

As the use of cannon improved in siege warfare, earth became yet more important as a means of absorbing the impact of cannonballs. Curiously, the ability to move vast quantities of earth allowed some fortification engineers to find work creating gardens.

Top tip: Save on labour, expense and time by digging the masonry of your castle walls from the ditches around the castle site.

Lay the foundations

Transfer the mason’s plan carefully to the ground

Using measured lengths of rope and pegs, it was possible to set out the foundations of a building in full scale on the ground. This was done by walking out the actions of a master mason’s drawing tools, his compass and set-square, to realise the plan. With foundation trenches dug, work began on the masonry structure. To save money, responsibility for construction was often deputed to a senior, rather than master, mason. The measurement of masonry usually used in the Middle Ages was the rod (16ft 6in, or 5m). At Warkworth, Northumberland, for example, the complex great tower is laid out on a grid of rods, probably for purposes of costing.

Medieval building processes are often well documented. In 1441–42, a tower at Tutbury Castle, Staffordshire was demolished and the plan for its successor laid out with ropes and pegs. The overseer, the Earl of Stafford, was for some reason dissatisfied. The king’s master mason, Robert of Westerley, was sent to Tutbury where he consulted with two senior masons to design a new tower on a different site. Westerley then left and over the next eight years a small group of workmen including four junior masons realised their new tower.

Senior masons could also be brought in to attest to the quality of work, as occurred at Cooling Castle, Kent, when the royal mason Henry Yevele surveyed work undertaken from 1381–84. He criticised departures from the original design and rounded down the bill.

Top tip: Don’t be cheated by your master mason. Make him design his building in such a way that it can be accurately costed.

Fortify your castle

Finish with sophisticated defences and high-spec carpentry

Until the 12th century, the fortifications of most castles were comprised of earth and timber. While stone buildings predominated thereafter, wood remained a very important material in medieval warfare and fortification.

Stone castles were commonly prepared for hostilities by the addition of fighting galleries along walls (termed ‘brattices’ or ‘alures’) as well as shutters that could be hung between battlements to afford the defenders protection. All these fittings were made of wood. So too were the heavy weapons that were used to defend castles, including catapults and heavy crossbows termed ‘springalds’. This artillery was generally designed by a highly paid professional carpenter, sometimes termed an engineer or ‘ingeniator’.

Such expertise didn’t come cheap, but it could be worth its weight in gold. This was certainly the case in 1266, when Kenilworth Castle in Warwickshire resisted Henry III for nearly six months, its catapults and water defences frustrating every attack.

There is even the occasional record of campaign castles being made entirely from wood, which could be transported and re-erected where needed. One such was built to cover a French invasion of England in 1386 but was captured on a ship by the Calais garrison. The castle was described as comprising a dense wall of timber 20ft high and 3,000 paces long. At every interval of 12 paces there rose up a 30ft tower capable of holding 10 soldiers, and there was some form of unspecified protection for gunners.

Top tip: Oak timber hardens with age after felling and is most easily worked when it is green. Pollarded trees (those with the upper branches removed) supply long clean limbs that can be easily transported and worked into shape with least labour.

Deal with water and sewage

Don’t forget the mod cons. You’ll appreciate them if the castle is ever besieged

It was essential that castles were provided with an effective water supply. This could take the form of one or more wells dug to serve particular buildings such as the kitchen or stable. It can be hard to appreciate the sheer scale of medieval well shafts without descending them. That at Beeston Castle, Cheshire has a shaft 100m deep, which is lined in cut stone for the first 60m.

There is also occasional evidence for the sophisticated use of water in domestic apartments. The great tower at Dover Castle possesses a system of lead pipes delivering water throughout the interior. It was fed from a well using a winch system and possibly from rainwater too.

The effective disposal of human waste was another problem confronting castle designers. Latrines were grouped together within buildings so that the shafts descending from them could empty out of a common outlet. They were also set down short corridors to contain smells and were often furnished with fixed wooden seats and detachable lids.

Castle latrines are often today popularly termed ‘garderobes’. In fact, the vocabulary for describing latrines in the Middle Ages was both colourful and broad. It included the words gong or gang (from the Anglo-Saxon meaning ‘the place to go’), privy and jake (a French form of ‘john’ or ‘johnny’).

Top tip: Ask your master mason to plan comfortable and private en-suite facilities off the principal bed chamber, following the example of Henry II at Dover Castle.

• 5 British castles with Romantic histories

Decorate as required

A castle doesn’t just have to be well defended – its high-status residents demand a certain swankiness too

Castles needed to be defensible in times of war but they also served as luxurious homes: the medieval nobility expected their accommodation to be both comfortable and well appointed. Throughout the Middle Ages these individuals travelled continuously with their attendant households, taking possessions and furniture with them from residence to residence. Important domestic interiors, however, commonly possessed permanent decorative fixtures such as stained-glass.

The decorative tastes of Henry III are recorded in particular and beguiling detail. In 1235–36, for example, he directed that his hall in Winchester Castle, Hampshire be painted with a map of the world and a ‘wheel of fortune’. This decoration has since been lost but the majestic interior does preserve the reputed round table of King Arthur – probably created between 1250 and 1280.

The wider setting of castles was also important for grand living. Parks were laid out for the jealously guarded aristocratic privilege of hunting, and there was a demand for gardens, too. The surviving building accounts for Kirby Muxloe Castle, Leicestershire reveal that its patron, Lord Hastings, began laying out the gardens at the very start of the building operations in 1480.

In the Middle Ages there was also a taste for rooms with fine views. One 13th-century group of rooms in castles that include Leeds in Kent, Corfe in Dorset and Chepstow, Monmouthshire, were named ‘gloriette’ after their splendour.

Top tip: Make sure the castle interior is splendid enough to attract visitors and friends. Entertainment can win battles without the danger of fighting.

John Goodall is an award-winning author, and architectural editor of the weekly magazine Country Life

This article was first published in the Christmas 2014 issue of BBC History Magazine