As the most important part of the castle, the keep would normally be built first, within a temporary protected enclosure. The curtain walls, gatehouses and ancilliary domestic buildings would follow. The keep had therefore to function not just as a defensive military strongpoint, but also to provide accommodation for the owner and garrison until the building work was completed. This gave the designer a few problems to solve.

To explore a square keep and understand the function of its various parts, we need to know something of the social norms, habits and customs of the age. Life for most people was a fairly public activity. The castle owner, be he the local lord or the king, had some private space, his solar, or study-cum-sitting room, and his bed chamber. The practice of the Christian religion was universal, the health of the soul being as important, or more important, than the health of the body. The provision of a chapel within the castle was essential, and the resident priest had his private room, as befitted someone of a religious order. Members of the lord's family and important guests had smaller rooms for their exclusive use, but for the rest of the inhabitants, eating, sleeping and working were communal activities.

To give you some idea about how life was lived in one of these buildings, I shall use an imaginary castle, (Let's call it something - how about Castle X ? Yes, really original. I may think of something better, later.), and take you on a guided tour.

You will have noticed by now that terminology is a somewhat inexact science and various bits get called all sorts of names. This doesn't matter as they don't mind. (They do get a bit miffed if you throw rocks at them, but more of that later.) A case in point is the word garderobe, which you can look up in the glossary, but means a latrine, or, as the monks had it, a necessarium. Some people will insist on calling these places lavatories, particularly Local Council Parks Departments, when we all know that the lavatorium was where you had a wash.

Okay, this beautifully crafted piece of artwork, Figure 1, shows the plan of the ground floor of Castle X. By ground floor, I mean, of course, the basement, cellars, etc., etc.

The black bits represent solid wall, the white bits are places where there aren't walls, (rooms or passages, etc.) and the grey bits are things like groined-rib vaulting, stepped window embrasures and other fancy bits that a Modern Architect wouldn't know how to spell. (Please note, I didn't say which Modern Architect.)

There are two points to notice, or rather two things missing. There is no external access to this floor, and the few windows are very small. Both these measures ensure that the only way for an attacking force to enter the building is through the front door. There is one flaw in the design, as the garderobes have to discharge their contents somewhere outside. Many castles have the exits at ground level for ease of cleaning and these are often large enough for a man to crawl up. Several invincible strongholds fell to an enemy with no sense of smell.

I can see that you are really eager to know about the prison. I put one in because they certainly existed. Ordinary felons would not have seen the inside of it though, hanging being the preferred penalty for just about every crime that you can think of and some you wouldn't want to think of. The occupant was usually a man of high rank who managed to get himself caught during a battle and was then held for ransom. It was in the chatelain's interest to keep such valuable commodities alive, healthy and reasonably happy. Not just to make sure of the ransom money, but just in case the boot was on the other foot on some future occasion.

But what about all the rooms down there? Well, people have to eat, and medieval folk did not go in for low-cholesterol diets, and fancy things like vegetables were only suitable for pigs and the really poor. And nobody had invented the refrigerator.So those nice cool dark cellars were a great place to store smoked hams, barrels of salted herrings, sacks of grain or flour, and maybe the odd barrel or dozen of wine and beer. They were also a good place to keep all those bundles of arrows and bits of rusty armour that might come in useful one day, so we'd better not throw it away.

A final point. The keep is a large building, and the walls are thick. They are thickest at the bottom. This helped to deter unpleasant visitors with battering rams. A further refinement was to add some batter. No, not the stuff you fry fish in, but an outward slope to the lowest few feet of wall. This made the battering-ram bounce off in an embarrassing manner. It was also good for slalom skiing practice in winter.

You probably thought the cellars were cold, dark and damp. Well this floor is - cold, dark and damp. And there's more of it.

There are some improvements on the cellars, though. We can (defensively) afford to have a few more windows, so we don't need a torch or candle (if we're the boss, because candles are expensive) all the time. When things get really cold, someone might light the fire. Of course, there is a fire - in the kitchen. If you are nice to the cook, he might let you sleep near the embers, otherwise it's the least draughty corner you can find. Windows with wooden shutters, yes. Double-glazing, single-glazing, or even curtains, no.

There are two major rooms on this floor. They are made by the simple device of sticking a cross-wall between the two side walls of the keep. The cross-wall makes for a stronger keep and helps to support the roof. Show me a keep without a cross-wall, and I'll show you a keep without a roof. In the case of Castle X (must think of a better name) the cross-wall also provides a handy place to hang the fireplaces.Fireplaces mean chimneys, and the chimney goes up through the wall. In some castles, the chimney went through the wall. At least the smoke didn't have to go out through a hole in the roof. At least in Castle X it didn't. Hmmm, and to think the Romans had under-floor central-heating.

Anyway, back to the rooms. The room with the oven built into the fireplace I shall call the kitchen. You will observe that the well (the circle near the top left) is inaccessible from this floor. This means that should the enemy gain entry to this floor, we can still get a drink if we're stuck upstairs. If the enemy have got this far, then this is probably a rather pointless security measure, but is does mean that the cook can be really nasty to someone and keep sending them up and down stairs to fetch water. Another place to put the well was somewhere in the inner bailey. The horses needed water too, and they didn't live in the keep. The second large room I shall call the hall, sorry, the Hall. This was where you ate breakfast and dinner (luncheon was invented later, about five minutes after canned processed meat), slept, and passed your free time in idleness and drunken revelry, you hoped. If you were unlucky, you also had to put up with the boss giving you your orders for the day, and if you were really unlucky, having to sit through Policy Review Committee meetings and in-house Refresher Courses On The Art Of Poniard Polishing.

There are other, smaller rooms. These may have provided a bit of privacy to some privileged members of the household. They certainly provided access to those nice arrow-slits for small sweaty archers to fire arrows through, should the need arise. On a technical note, if you want to fire arrows through a hole in a twelve foot thick wall, you have problems. You want the outside of the hole to be small, so that you can fire out, but others cannot fire in, and you want to be able to see, and fire at, a reasonably wide area. They solved both problems. See if you can work out how.

There are also garderobes. Enough on this subject save to mention the cunning way in which things are arranged so that the shafts are grouped together to make emptying easier, but do not interfere with each other.

Then there's the front door, or as the guide book says, "The Entrance To The Keep". The doorway itself is protected by - doors. And perhaps a portcullis as well. Castle X has two sets of doors. If any of the enemy get between the sets of doors, you can fire arrows at them from the guardrooms on either side. To even get to the doors, the enemy has to get through the fore-building. This means climbing endless flights of stairs, being shot at on the way, having to turn through right-angles so that their unshielded sides can be shot at, and maybe having to contend with a few more portcullises and the odd draw-bridge.Portcullises and draw-bridges are sadly lacking at Castle X, but there are plenty of stairs, turns and places to be shot at from. It was tough being a milkman in those days.

We are now getting to the more private areas of the keep. There is the chapel and the priest's room next door to it. And there are two more large rooms. We can let our hair down even more on the subject of window size, but there are still arrow slits. We can imagine the large room from which the chapel opens as a place of relative peace and quiet. This would be a good place for the women of the household to get on with the things that women of this time were expected to get on with. Sewing and gossip, and balancing the accounts. Setting the menu for the next day's meals and writing the shopping list. Perhaps the other large room is the private room of the lord's wife, the lady of the household. There is a mural chamber with an arched entrance and two windows. Is this her bed chamber, or a place for quiet contemplation ? A place for embroidery while her maids get her up to date with the castle news. A favourite spot from which she can look out over the gently rolling hills and chequered dales of her demesne. And is that a knight, galloping up the road, the sun glinting on his armour, pennant fluttering from his lance head, and a huge arrow pointing at him, labelled "Romantic Daydream" ?

One of the major rooms on this floor would be the lord's solar, or day room. Solar meaning "sunny and bright with not a cloud on the horizon" or something vaguely like it.This is where he would have paced up and down dictating letters, death sentences, and his autobiography. I say dictating because the lord of Castle X can't read or write very well. This is where the priest comes in handy again. Let us dispel a myth. It is said that King John did not sign Magna Carta, he sealed it. And he sealed it because he was illiterate. This was not necessarily because he couldn't write his own name or that the people who were meant to read it, couldn't. (Read it that is, not write "King John".) Putting an enormous great blob of decorative wax on the bottom of an official document is what the bottoms of official documents are for. Ask any civil servant. And a king is nothing if not a civil servant. Unless he happens to be a Cruel And Merciless Tyrant.

The other room may have been the lord's bed-chamber. It would have contained a bed, a large wooden chest for clothes, a chair, a table, and perhaps one of those big wrought-iron candle-sticks.

This is the first time in this piece that I have mentioned furniture, because I'm more interested in the buildings themselves. People had furniture. They just didn't have a lot of it. I have enough furniture in a modest three-bedroomed house to make even a King John jealous. One good thing about the furniture of those days, though, it was all antique. (A small prize for anyone who can think of a word for beds, tables, chairs etc., that is not spelled "furniture".)

Well, not exactly on to the roof, rather on to the wall walk around the roof. Or in the case of a real castle, around that big hole where the roof used to be. Roofs on the tops of square keeps were like the roofs on square houses. Fact. What else would they be like ? If you don't believe me go to France, where some of their castles still have roofs. The newel stairs would have had roofs too. I have shown them with miniature versions of the main gables. Or they may have been flat, with corner turrets sitting on top. Or they may have been conical. To find out for sure, you must look for Clues In The Masonry.Be assured, when it comes to castles, the Masonry Cannot Lie. It just tells whopping great fibs, and does its darndest to confuse you. There is a reason why Castle X is relatively easy to interpret. It's brand, spanking new. Over the next few hundred years it will have other owners. They will be subject to the whims of Fashion. They will have Ideas. They will make Improvements. And historians, antiquarians and archaeologists will have a really good excuse to be rude about each other.