I love castles.

I mean I really love castles. I’ve enjoyed climbing over ruins and up spiral staircases for as long as I can remember – and since my mum was a history teacher, that was a good thing because we visited a lot. I still do with my own children. The more remote and desolate the better, preferably on a cold autumn day with a thermos so I can sit and think up stories.

So when I decided to write a novel, I knew it was going to be medieval, and it had to involve a castle, preferably with turrets and ramparts and battlements to spare. Think Carcasonne, only bigger. Unfortunately, with my story set around Norfolk and Essex in 1067, this wasn’t exactly plausible. The Normans started building in stone fairly soon after the Conquest – replacing the wooden motte and bailey style fortresses they initially threw up in a matter of weeks – but there was still a limit as to how much they could have achieved in ten months.

So I might have exaggerated a little. But only a little. Castle Etton, where my heroine Aediva is taken to confront William FitzOsborn, is a work-in-progress, standing side-by-side with the old Saxon fortress. The masons are still at work on the stone curtain walls, though the new keep is finished, a two-storey stone building that might reasonably have been built for one of the Conqueror’s more important barons.

Now I’m at work on my third book, however, I have a whole new castle-based challenge. This time my heroine Juliana is the chatelaine of a small, slightly ramshackle fortress on the Severn that suddenly finds itself besieged by Matilda’s forces, led by my Frankish hero Lothar, during the Anarchy.

So how would a castle have looked in 1147?

For a start, due to their weight, stone castles were built either on the flat or on natural hills, located at strategically important positions such as besides rivers or ports, in towns, or at crossroads. The actual design needed to be practical as well as intimidating, with moats, ditches and drawbridges providing a first line of defence, thick walls to prevent undermining, narrow slit windows to provide safe vantage points for archers, and slanted roofs to deflect missiles hurled by siege engines. Even the insides of the castle were defensive. Beyond the bailey, there was often another ring of walls to protect the keep, itself accessed via the first floor. Spiral staircases were also designed to favour those defending the castle, and there were even hidden doors to aid escape.

Given all this, it’s hard to imagine a castle serving as a home too, but that’s the side of the castle I’m really interested in. Castles were effectively microcosms of towns, with blacksmiths, carpenters, cooks, as well as soldiers all living together, frequently under the same roof. Once my siege is over my hero and heroine need to find a way to live together, preferably without killing each other, to rebuild a home as well as a fortress, hopefully falling in love along the way. Now I just have to work out how…