CHRIS KOENIG talks to Oxford classics don Harry Sidebottom about his debut as a writer of historical fiction with the first part of a projected trilogy

Lucky people — or should that be clever and wise people? — seem to have the ability to put into practice that dictum many of us learned long ago from the lips of well-meaning teachers: find out what you like doing in life, then persuade someone to pay you to do it (though as some wag said, they put it differently in girls' schools).

Meet Harry Sidebottom. For many years I have known him as an Oxford University classics lecturer. Now he has suddenly metamorphosed himself into a writer of popular fiction, using as his subject matter his own area of erudition: namely ancient history.

First fruits of his pen (apart from an academic book, Ancient Warfare: A Very Short Introduction, published by the OUP in 2004) is Fire in The East (Penguin Group, £12.99), volume one of a trilogy of derring-do called Warrior of Rome. Over a glass of wine at his local pub, the King's Arms in Woodstock, he said: "I was lucky, I suppose, because I already had an agent, thanks to my academic work; and he said it would be worth having a go. So I spent six weeks one summer vacation producing three chapters and a synopsis. I bunged them off. Then months went by and I heard nothing — until the fairy tale bit began: the telephone rang and out of the blue I heard that Penguin had bought it."

He then set about the task of fulfilling the contract with almost military discipline. He hired a spare room in a friend's house in order to be out of the way of his wife, Lisa, and two small children — four-and-a-half-year-old Tom, and one and-a-half-year-old Jack — and turned up there each morning at nine, as though he were clocking into an office job.

"The amount of money Penguin paid me helped," he explained modestly, "and both St Benet's Hall, where I am a Fellow, and Lincoln College, where I am a lecturer, were very good about letting me off some teaching."

The result of his lonely labours is something that takes you out of the 21st century and into the mind of a hero who happened to live his life in the third century AD; it is a 'laddish' sort of book, suitable for reading poolside in Marbella, yet it is thought-provoking and strangely relevant to our times too. Little wonder, perhaps, that it has already sold about 20,000 copies in hardback — an extraordinary achievement for a debut novel.

In 255AD, when the book begins, the Roman Empire was crumbling round the edges, with the most potent threat to central authority coming from the East, from the Sassanid empire in Persia. Our hero, the Anglo-Saxon Marcus Clodius Ballista, is sent off to the border city of Arete, on the west bank of the Euphrates, to shore up its defences and to face down the enemy.

"Ballista means 'War' and Arete means 'Virtue', so a sort of siege of Virtue is involved here," Dr Sidebottom remarked.

He said that the fictional town of Arete is modelled on the ancient town of Dura-Europos which stood on the present-day border between Syria and Iraq, adding: "For the benefit of the plot I have played around with the topography of Dura and the siege works, mainly simplifying them."

On page one the book states baldly: "War is hell". So why, I asked, is Dr Sidebottom so fascinated by it? After all, his own background is not military, though his father, a racehorse trainer in Newmarket, served in the last world war.

"I suppose I must answer with a cliché: it brings out the best as well as the worst in men." Then we touched on the recent, 21st century, Iraq war, thinking of examples of good and bad behaviour there.

And what do fellow academics think of his becoming a writer of popular fiction? Dr Sidebottom says in a note at the back of the book: "When I told my colleague Bert Smith, the Lincoln Professor of Classical Archaeology and Art at the University of Oxford, that I was writing a series of novels set in the second half of the third century AD, he congratulated me on picking a period about which so little is known for sure that no one could prove me wrong."

Dr Sidebottom told me: "They were mainly very encouraging — though there was talk about how perhaps I should write under a different name. Why on earth should I do that, I thought to myself."

In fact it was another academic and Oxfordshire author, Robin Lane Fox, who whetted his appetite for ancient history in the first place with his book on Alexander the Great.

As for the wisdom involved in the business of getting someone else to pay you to do what you enjoy doing anyway, he said that many Romans, just like many of us in the modern world, were forced to do what they don't like doing. The hero of the book, for instance, set out to liberate a place and ended up destroying it.

"He would have preferred to have been left alone," said Dr Sidebottom.

Harry Sidebottom is at Woodstock Celebrates Books on Saturday, October 11, at noon.