Marc Morris's passion for castles began at an early age, writes Phillippa Boston.

The author of Castle (PanMacmillan £18.95) and presenter of the accompanying Channel 4 series is completing his doctorate at Merton College, Oxford, but was born in Kent.

Kent, being the first stop for potential invaders coming across the English Channel, is packed full of castles, and Morris's parents encouraged their son's interest by taking him to visit as many as possible.

Marc Morris talks about castles to pupils at Oxford's Dragon School

Morris chose to study history for his first degree and MA at King's College, London, and soon realised that specialising in the medieval period would give him carte blanche to re-explore his boyhood hobby. Soon it became work as well as play. His studies led him, in 1998, to Oxford, to pursue a doctorate on the 13th-century Earls of Norfolk.

I caught up with a very busy Marc Morris as he was giving a talk on castles to the boys and girls at the Dragon School in North Oxford. I asked him how he managed to get from a thesis on the Earls of Norfolk to a series on Channel 4.

"In April 2001, an email was sent out to various university departments looking for people who had recently completed, or were about to complete their doctorate, who would be interested in presenting a television series."

Morris applied late, found they were still looking for the right candidate, had a screen test and got the job. Two years later, he is gracing our screens on Thursday evenings.

The TV series, like the book, follows the premise that one can analyse a specific period in British history by looking at the castles that were built at that time. Take a prime example of a castle and one gains an insight into its contemporary society.

The cover of the book is graced by Bodiam Castle in Kent, one of my favourite castles, which illustrates this very well. It has all the cosmetic characteristics we would expect from a castle, but, as Morris points out, is actually a bit of a sham. As a defensive structure, its 'false' gatehouse at the front and its easily breached back gate make it easy to take in battle.

But Bodiam, built by one of our great soldiers, Sir Edward Dallingridge, in the 14th century, was built not to defend an England that was enjoying a period of unprecedented peace, but to show that same England what an important man Dallingridge was: "He didn't need a fortress, because England was such a peaceful place. He needed to show off."

Morris points out that structures which want to proclaim their importance to the populace outside often display the characteristics that we would normally expect from a castle, even though they have nothing to do with defence -- including many Oxford colleges: "No one at my college was expecting trebuchets (instrument of siege) to turn up and start slinging things at them. These things say 'we're important', 'we matter'."

Wherever Morris looks, he sees more information to be read within the castles that he loves so much. The string of castles built by Edward I in the 13th century to subdue the Welsh -- including Caernarfon, Conway and Harlech -- are built as highly efficient defensive structures, unlike Bodiam. Their purpose was to leave the Welsh in awe of the English king who now ruled over them, and to therefore discourage their wicked Welsh ways of yore.

Caernarfon, the greatest of them all, said to be the birthplace of the Emperor Constantine, is replete with echoes of Constantinople and Christian imagery.

Here, Morris points out: "Edward I was proclaiming himself a 'new Constantine', a Christian emperor, using symbols of imperial power, such as the carved, stone eagles on the towers to reinforce this message."

There is no shortage of material in Britain for any number of television series on castles, but Morris says he is looking forward to moving on to another aspect of medieval British history. And what does the future hold for Morris -- more television, or more research?

"As much as I love history, my love is not in the research of it. Research is just you and your material. I enjoy the energy of television, the intelligent interchange with everyone involved, the stimulation of others."

He and Channel 4 will be plotting their next conquest, of which we will hear more details in the near future.

Castle: A History of the Buildings That Shaped Medieval Britain is published by Channel 4 Books at £18.99. The final programme in the Channel 4 series is on June 19 at 8pm.