As restoration work to stop Pisa's famous tower from toppling over nears completion, an ex-infantryman has revealed for the first time how he saved it from US artillery during the second world war. Rory Carroll reports.

They started the final phase of shoring up the Leaning Tower of Pisa on Tuesday morning, around the same time that Leon Weckstein, 6,000 miles away in California, ate one last piece of birthday cake and turned in for the night.

Workmen clamped giant steel braces around the monument and adjusted the weights hanging from it. Gravity and soggy footings were making the tilt too sharp and threatening to collapse 150,000 tonnes of Renaissance stone on top of tourists. Disasters apart, in a few months Italy will declare one of the wonders of the world saved and open for business.

What the glitterati who assemble to celebrate will not realise is that if it was not for a terrified 23-year-old American soldier, it would not exist today at all.

Towards the end of the second world war, Weckstein was one of the GIs struggling through the marshy ground that surrounds Pisa, advancing on the stubborn Germans who still occupied the Tuscan town. Had he uttered just six short words -"This is Able George One. Fire" seconds later an infantry division with batteries of 155mm cannons and a destroyer moored offshore would have blasted the tower to dust. But two things conspired to stop him - his fear and the tower's beauty.

More than half a century after he lowered his telescope on that sweaty afternoon, Weckstein, now 79, has decided to tell his extraordinary story for the first time, in a book. Joseph Heller's Catch-22 it is not. Madness and death certainly play their part, but what ultimately triumphs, against all the odds, is the appreciation of beauty.

The omens were not good that night in July 1944 when a booming voice called out for Sergeant Weckstein across an olive grove criss-crossed by slit trenches full of exhausted GIs.

Every bend of road, every farmhouse and every escarpment seemed to be booby-trapped or occupied by groups of obstinate German defenders. Their orders were to delay the allies at all costs. Field Marshal Kesselring had introduced his new weapon, the Nebelwerfer: a multi-barrelled rocket launcher that hurled 20 or more missiles in rapid succession from an adapted truck. Screaming Mim, the Americans called it. The final two-and-a-half miles into Pisa had become a killing zone. As the number of American dead and wounded mounted in the mud the advance was in danger of stalling.

What their top brass could not figure out was how the Germans could be so accurate in such flat, coastal terrain. They had to have a vantage point but where was it? Intelligence units surveying the terrain ruled out every spot except one - a monument 185ft high the infantry "grunts" called the tiltin' Hilton.

So it was that Weckstein was roused from sleep and delivered to Colonel Woods, who gave him the most dangerous mission of his war: to take a radio man and get as close to the tower to find out if the Germans were inside.

Like many GIs, Beckstein, a young man from the suburbs of Los Angeles, had never heard of the leaning tower of Pisa. The generals had, but if enemy activity was detected they were not going to sacrifice men for a chunk of masonry, no matter how old. Only two months earlier allied bombs had obliterated the monastery at Monte Cassino which the Germans had made a fortress.

"If you see anything that looks at all suspicious, don't wait. Call down fire," ordered Woods. Waiting for the signal were inland gun batteries and the destroyer offshore.

This week, the laconic Californian voice at the end of the phone quickened at the memory: "There wasn't a single doubt in my mind that I really was about to do the deed, to direct sallies of doomsday fusillades."

What Woods and the rest of the 91st Infantry Division's top brass did not know was that they were entrusting one of the war's most fateful observation missions to a man rejected by the navy for being short-sighted. "In 1942 the navy had told me to go away and eat carrots for six months," says Weckstein. "Then the infantry took me - but they take anyone."

Excited and terrified, the young infrantryman ate a K-ration fruit bar, slurped strong, black coffee, and picked up his radio man, a taciturn Ohio guitar-player called Charles King. They smeared mud on their faces and headed out into the hot, muggy dawn.

"Our bodies bent low to the ground, we crouched and stumbled slowly along the perilous way towards our objective for what seemed like an eternity. King had begun to sweat conspicuously. He had that clumsy radio to lug around, and I felt sorry for him."

After an hour they reached an olive grove threequarters of a mile from their target. Trying to ignore his sweat, itching and fleas, Weckstein raised the telescope he had found in an abandoned house months before.

"I focused first on the highest point, the broad circular campanile of the tower. I could easily make out the shadowy silhouette of the old bells, quiet now, but nothing moved. I took my time training the 'scope ever so slowly up, down, and across each elaborately ornamented balustrade, attempting to discern anything that might be hidden within those black recesses and arches."

The grace and beauty hynoptised the former supplies clerk. He momentarily forgot the friends killed by shells almost certainly directed from the monument. He snapped out of it and again scanned, "hoping against hope for even the slightest sign of a possible target". Waves of heat suddenly turned the tower into a vibrating mass, "as if I were attempting to look through a bowl full of wiggling Jello".

Anger and fear swelled. "Finish the damn job! I yearned to blow it to smithereens, but as yet I had seen nothing move. Not a damn thing moved." He tried to will himself to do it. He imagined himself to be an evil, Nazi solider hiding in the sixth level, laughing at his victims. "The hell with orders, I thought. I'll just go ahead and fire."

He turned to the radio man and the words were on his lips but they would not come. Seconds turned to minutes and still he could not do it. The hypnotic spell had not been broken after all. The tower, the neighbouring cathedral and baptistry, were too beautiful.

Weckstein was still transfixed when German shells burst overhead. It was too late now to do anything except run. The two men raced back to their lines under heavy fire. The generals decided to spare the tower. To this day it has never been established whether the Germans were inside. Weckstein turns wistful. "You know something? I've had 50 years to think about it, and I'm pretty sure they were."

Through My Eyes: 91st Infantry Division in the Italian Campaign, 1942-45, is published in the Hellgate Memories Series