Over 60 heads of state and government gathered -- silent, somber and reflective -- for a ceremony at the Tomb of the Unknown Soldier, the mute and powerful symbol of sacrifice to the millions who died from 1914-18.

They heard high-school students recalling the joy felt by soldiers and civilians alike when the fighting finally stopped at 11 a.m. on Nov. 11, 1918. And they heard the commemoration's host, French President Emmanuel Macron, warn about the fragility of peace and the dangers of nationalism: a theme that seemed directed, at least in part, at US President Donald Trump, who listened stony-faced.

"The traces of this war never went away," Macron said.

"The old demons are rising again," he intoned. "We must reaffirm before our peoples our true and huge responsibility."

The Paris weather -- grey and damp -- seemed aptly fitting when remembering a war fought in mud and relentless horror.

The commemorations started late, overshooting the centenary of the exact moment when, 100 years earlier at 11 a.m., the eerie silence of peace replaced the thunder of guns on the Western France. As bells marking the armistice hour started ringing out across Paris and in many nations hit by the four years of slaughter, French President Emmanuel Macron and other leaders were still on their way to the centennial site at the Arc de Triomphe.

Under a sea of black umbrellas, a line of leaders led by Macron and his wife, Brigitte, marched in a stony silence on the cobbles of the Champs-Elysees, after dismounting from their buses.

Trump arrived separately, in a motorcade that drove past two topless protesters with anti-war slogans on their chests who somehow got through the rows of security and were quickly bundled away by police. The Femen group claimed responsibility.

Last to arrive was Russian President Vladimir Putin. German Chancellor Angela Merkel was positioned in pride of place between Trump and Macron, a powerful symbol of victors and vanquished now standing together, shoulder to shoulder. Overhead, fighter jets ripped through the sky, trailing red, white and blue smoke.

The geographical spread of the leaders in attendance showed how the "war to end all wars" left few corners of the earth untouched but which, little more than two decades later, was followed so quickly and catastrophically by the even deadlier World War II.

On the other side of the globe, Australia and New Zealand held ceremonies to recall how the war killed and wounded soldiers and civilians in unprecedented numbers and in gruesome new, mechanized ways.

Those countries lost tens of thousands of soldiers far away in Europe and, most memorably in the brutal 1915 battle of Gallipoli, in Turkey.

In Paris, the jewel that Germany sought to capture in 1914 but which the Allies fought successfully to defend, the armistice commemorations were being followed by the afternoon opening of a peace forum pushed by the host, French President Emmanuel Macron.

Trump will be the most notable absentee at the forum, where Macron's defense of multilateralism will take center stage. Trump lives by an "America First" credo, and plans to visit the American cemetery at Suresnes on the outskirts of Paris before heading home.

On Saturday, he was criticized for canceling a visit to the Belleau Wood battleground northeast of Paris because of rain.

In the four years of fighting, remembered for brutal trench warfare and the first use of gas, France, the British empire, Russia and the United States had the main armies opposing a German-led coalition that also included the Austro-Hungarian and Ottoman empires. Almost 10 million soldiers died, sometimes tens of thousands on a single day.

The United States came late to the war, in April 1917, but over 1 and half years it became a key player in the conflict and tipped the scales for the allies. When the war ended on Nov. 11, 1918, the US armed forces was on the cusp of becoming the major military power in the world.

Even though Germany was at the heart of provoking two world wars over the past century, the nation has become a beacon of European and international cooperation since. 

On Sunday, Chancellor Angela Merkel met with the head of the United Nations, born from the ashes of World War II, and the president of Serbia. It was a Serb teenager, Gavrilo Princip, who assassinated the Austro-Hungarian crown prince in Sarajevo in 1914 to set off events which led to the outbreak of war. (AP)