Image caption Piero della Francesca is believed to have painted the fresco in 1467-68, in what is now the Civic Museum

A chance discovery has brought to light the little-known story of how a British Army officer risked a court martial in wartime Italy to save a painting the author Aldous Huxley once described as "the greatest picture in the world".

I opened a dead man's suitcase in Cape Town and was transported from today's Africa, via World War II Italy, to Renaissance Tuscany.

Inside I found a story of high art, bravery and love, all the more powerful because it is a story not widely known.

I was on Long Street, a boisterous city-centre shopping artery, exploring the upper floors of Clarke's, a venerable bookshop staffed by bibliophiles who lovingly tend roof-high displays of new titles.

Climb up the stairs at the back and you enter a booky world almost extinct in today's era of online, search-engine rigour.

Here second-hand works await discovery, all meticulously catalogued, some preciously protected in glass-fronted cabinets.

Staff walk to and fro across creaking floorboards and up half sets-of-stairs linking a maze of attics, all crowded with books.

Graham Greene was my research target, more specifically his links with Tony Clarke, founder in 1956 of what is arguably Africa's finest bookshop.

Clarke died in the 1980s but his effervescent successor, Henrietta Dax, allowed me to look through his remaining papers, higgledy-piggledy in a brown leather case.

Fighting tradition

Image caption After WWII Tony Clarke founded what is arguably Africa's finest bookshop

Of Greene I found nothing but, as so often with research, the letters, notebooks, diaries and photographs drew me off down another thrillingly unexpected by-way.

The records were of a man who came of age in WWII.

There were doodled maps of El Alamein and photographs of Clarke as a young subaltern sitting smartly to attention in the Middle East in 1942 alongside fellow members of the Royal Horse Artillery.

The RHA is one of the army's smartest units - its gunners fire the ceremonial salutes in Hyde Park - and Clarke belonged to its oldest battery, the Chestnut Troop.

Its fighting tradition is proud, no more so than against Rommel's Afrika Korps and later on the long Allied slog up Italy.

The snapshots of Clarke's campaign are framed in black and white: here lean, sun-tanned Tommies lark about on a Mediterranean beach, there stones ring the grave of a fellow officer, a chum, on an Italian hillside.

A reconnaissance photograph of Monte Cassino shocked me.

Clarke was not involved in the fight to dislodge the Germans from its hilltop monastery but in his diary he describes how shocked he was as he drove underneath ancient walls hideously disfigured by bombardment.

It may have influenced what Clarke went on to do.

As the Allied advance continued, his unit took up a firing position near the town of Sansepolcro.

Unlike other famous Tuscan towns that are perched on hilltops, it lies down in a valley. I went there myself in the 90s and found its location memorably unmemorable.

It was standard then for allied artillery to soften up towns before ground troops went in, and Clarke was the officer responsible for Sansepolcro. His guns dug themselves into their firing pits, his gunners prepared their ammunition stocks.

But then some faint bell rang in his mind, a bell belonging to an age far from the madness of war.

Clarke - English, gay, art-loving - remembered an essay by Aldous Huxley. The author had not been shy with his superlatives, saying he had discovered what he called the world's "best picture".

Image caption Clarke's was established in 1956

In fulsome terms, the essay described the incredible power of The Resurrection, a fresco masterpiece by the Renaissance maestro Piero della Francesca.

"We need no imagination to help us figure forth its beauty,'' Huxley wrote. "It stands there before us in entire and actual splendour, the greatest picture in the world."

Clarke may not have remembered every detail of the essay but, just as his guns started firing, he remembered one key fact.

The Resurrection was located in Sansepolcro.

I can only imagine the risk he then took by withholding his order to fire.

He later said his commanding officer had come on the radio urging him to get on with it so he had to stall for time, peering at the town through binoculars and assuring his commander that he could see no German targets to go after.

Image caption Members of the Royal Horse Artillery on manoeuvres in Egypt in 1936

It was a brave action. Had Allied infantry been ambushed as they advanced on Sansepolcro, his court martial would have been brutal.

But, for the love of art, he kept the guns silent. The Germans fled and the town was liberated the following day without any damage to the 500-year-old work of art.

As I left his shop, I thought of Clarke. Nowadays such an act would be spread across newspapers and picked over by script-writers.

But all that remains today is a Sansepolcro suburban street named in his honour, a few references in travelogues written long after the war and a suitcase of memories at the foot of Africa.

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