The Battle of the Bulge was the last German offensive of World War II, and the Siege of Bastogne the scene of a heroic defence by American paratroopers.
Seventy-five years on, the Belgian town is hosting a weekend of colourful re-enactments followed by solemn ceremonies of remembrance.
Veterans, historians and military enthusiasts will join international officials to mark the now legendary close quarters battle on a snowbound wooded plateau.
Bastogne's relief in late December 1944 by General George "Old Blood and Guts" Patton helped seal his reputation as one of America's military giants.
But the out-gunned paratroopers of the 101st Airborne -- who held the pocket for a week against advancing German armour -- also claim a share of the glory.
The Belgian town of Bastogne, close to the Luxembourg border in the Ardennes hills, is the focus of the commemoration, as it was of the fighting.
On December 16, 1944, German forces -- which had been falling back before the Allied advance from France since June's D-Day landings -- counter-attacked.
Their goal was to seize the port of Antwerp to deny it to Allied resupply ships, and five of the roads north converged on the small southern town.
By December 20, the battle-hardened but lightly-armed US paratroopers were surrounded and a German Panzer general demanded their surrender.
"Nuts!" was the one word reply from the US commander, and the ensuing week-long siege lasted until Patton's Third Army was able to come to the rescue.
On Sunday, hundreds of re-enactors in period uniforms from both sides will recreate sequences of the battle outside the hamlet of Hardigny.
And on Monday, dignitaries will gather at the Mardasson Memorial to the thousands of American dead for the official ceremony of remembrance.
Belgium's prime minister, Sophie Wilmes, will be joined by US Secretary of Defense Mark Esper and Germany's President Frank-Walter Steinmeier.
Poland's President Andrzej Duda will also be there, along with envoys from Britain, Canada and France.
In the afternoon, the convoy will cross the border to the Luxembourg Military Cemetery and Memorial in Hamm, Patton's last resting place.
The general died in a road accident during the 1945 occupation of a defeated Germany, but was buried in the Ardennes with comrades from his famous victory.
There they will be received by Luxembourg's Grand Duke Henri and Prime Minister Xavier Bettel.
Mathieu Billa, historian director of the Bastogne War Museum, told AFP that the then 59-year-old Patton reached the summit of his glory when he relieved Bastogne.
The 18,000 encircled men had fought bravely against enormous odds, but risked being overrun.
- Artillery barrage -
The overall Battle of the Bulge would rage across the Ardennes for six weeks, until the Allies prevailed against the Germans in January 1945.
Between 15,000 and 20,000 German troops died, against between 10,000 and 19,000 Americans.
And 3,000 Belgian civilians perished under artillery bombardments or in massacres carried out by the Waffen-SS in villages like Houffalize.
The Bastogne fighting has been recounted by veterans interviewed for the book and the television series "Band of Brothers" and entered US military folklore. But 75 years on the number of former combatants and witnesses who can attend ceremonies is declining, and Belgium's War Heritage Institute has invited them.
There will be Belgians and Americans and also Germans "because we must appreciate history from both sides with a view to reconciliation," said spokesman John Osselaer.
On Sunday, 10 serving members of the 101st will read accounts of the fighting in the Jacques Wood where their predecessors dug foxholes in the snowy ground.
"Our gratitude to the young Americans who fell on Ardennes soil is eternal. We owe them our freedom," said Bastogne's Mayor Benoit Lutgen.