Veterans are gathering to remember the Battle of Monte Cassino - one of the toughest battles fought in Western Europe in World War II, and still one of the most controversial.
The allies were fighting their way up from southern Italy towards Rome, and the monastery of Monte Cassino stood at the strongest point of a powerful German defensive line.
The battle took four months, and by one estimate it left a quarter of a million dead or wounded.
"Only the bloodbaths of Verdun and Passchendaele, or the very worst of the Second World War fighting on the Eastern Front, can compare to Monte Cassino," writes the author of a recent book on the battle, Matthew Parker.
"The largest land battle in Europe, Cassino was the bitterest and bloodiest of the Western Allies' struggles with the German Wehrmacht on any front of the Second World War.
"On the German side, many compared it unfavourably with Stalingrad."
The German defensive line, the Gustav Line, was drawn along rivers backed by steep mountains - icy in winter and baking in summer.
"The seemingly unending succession of mountain ranges, ravines and rivers of the Italian terrain demanded the soldierly qualities of fighting valour and endurance in a measure unsurpassed in any other theatre of war," wrote the British General Harold Alexander in his memoirs.
The German commander, Lieutenant-General Fridolin von Senger und Etterlin, wrote: "We found that divisions arriving from other theatres of war were not immediately equal to the double burden of icy mountain terrain and massed bombardment."
General Alexander sought unsuccessfully to have the death penalty reinstated for desertion as the battle wore on.
The allied forces were very mixed. As well as Americans and British, there were French from North Africa, Indians and Gurkhas, New Zealanders, Canadians and Poles.
Sometimes the generals disagreed, sometimes their actions were badly co-ordinated. Often they ordered attacks that were hugely wasteful of human life.
Professor Richard Holmes of Cranfield University has written for BBCi History that Italy would be most easily mistaken as Europe's "soft underbelly" (as Winston Churchill called it) by people whose maps lacked contours.
"There was, for a start, no prospect of Italy ever becoming more than a subsidiary theatre," he says.
"While the application of brute force might take the allies steadily northwards, it was unlikely that their advance would ever be quick or easy. The best that they could hope for would be to tie down German troops who might be usefully engaged elsewhere."
The question has always been asked: Was the bloodshed of Monte Cassino worth it?
There were four main battles, in January, February, March and May.
The second was preceded by the bombing of the 1,400 year-old Benedictine monastery of Monte Cassino, the third by the obliteration of the town of Cassino.
In the fourth it was the Algerian, Moroccan and Tunisian troops of the French Expeditionary Corps who made the decisive breakthrough, in the Aurunci mountains south of the Liri river, forcing the Germans to withdraw.
They had also made a major impact in the first battle, in January, but the French general Alphonse Juin never got the support he wanted for a wide flanking movement through mountains to the north and west of Cassino.
Matthew Parker says it is the great "what if?" of the Cassino story.
If he had got that support - either then or later when General Francis Tuker of the 4th Indian Division was urging a similar strategy - perhaps the resulting bloodbath could have been avoided.
Monte Cassino, The Story of the Hardest-fought Battle of World War II, by Matthew Parker was published by Headline in 2003.