At the start of September 1914, after just one month of war in Europe, the German army were at the gates of Paris. The word on the street was that emperor Wilhelm II had already booked a dinner table on the Champs-Elysees.
Poorly-equipped and badly-organised, the French army was in dire straits, retreating on all fronts alongside their newly-arrived British allies.
But in one final surge, they somehow managed to halt the German advance and change the course of World War I in the Battle of the Marne (September 6-9) -- talked of as a "miracle" by those who witnessed it.
The Germans took the town of Senlis, 60 kilometres (35 miles) from Paris, on September 1. The next day, German Ulhan cavalrymen were seen on the outskirts of Meaux, just 40 kilometres from the capital.
The Central Powers looked set to achieve the goals of the so-called "Schlieffen Plan", which aimed to crush the French army in just six weeks -- before British reinforcements could arrive -- and then attack Russia on the eastern front.
The French, by contrast, were in full retreat, and Paris swirled with fearful gossip and rumours of looming German troops.
General Joseph Joffre, commander-in-chief of the army, and war minister Alexandre Millerand wanted to declare Paris an "open city" -- essentially abandoning all defences in the capital. They were overruled by Prime Minister Rene Viviani, who ordered the formation of an autonomous defence force for Paris.
On September 2, the government relocated to Bordeaux, taking with it the central bank's gold. The art collections of the Louvre were moved to Toulouse.
Over half a million Parisians joined the exodus.
But on September 3, French reconnaissance pilots noticed something odd: the right flank of the German army, previously making a beeline towards Paris, had suddenly lurched to the south east.
- German error -
German command mistakenly believed the French army to be in haphazard retreat, and pursued it towards the River Marne, east of Paris, to inflict a decisive defeat.
But by changing direction, the German First army commanded by General Alexander Von Kluck inadvertently presented its right flank to French forces massed on the outskirts of the capital. It was an error that Joffre immediately seized upon to launch an attack between Senlis and Meaux.
In order to transfer troops to the front, General Joseph Gallieni, Paris' military commander, requisitioned 700 Parisian taxis. The now-legendary "Marne taxis" allowed thousands of soldiers to mobilise swiftly, boosting morale and scoring an early propaganda victory for the French.
The main battle took place over three days. On paper, the two sides were almost equally matched: 81 German divisions against 80 French and British.
But historians suggest over-eagerness by German generals, who had just overseen three weeks of almost non-stop marches eastwards, may have turned the tide in favour of the Allies. Exhausted and hampered by logistical problems, some 750,000 German servicemen faced off against half a million well-rested and organised French and British troops.
- Beginning of trench warfare -
As Von Kluck pressed his men forward, he allowed a 35-kilometre breach to form in the German line, which was quickly filled with onrushing Allied troops.
The Germans were at risk of encirclement and generals in Berlin ordered troops to retreat to the river Aisne, 100 kilometres to the north, confirming a French and British victory.
As for the balance sheet of casualties, numbers vary wildly between sources. It is generally estimated that close to 100,000 troops from each side died, and at least twice that number were wounded.
In the weeks that followed, a stalemate developed that would persist for the rest of the war. Both armies were too exhausted and damaged after one month of bloody battles to launch another meaningful offensive.
After the so-called "Race to the Sea", where each side tried to outflank their enemies to the north, the Western front stabilised in November in a continuous line cut from the North Sea to Switzerland.
This was the start of the war of attrition -- or trench warfare -- that seared itself into Europe's collective memory as the abiding image of World War I.
No soldier on either side of the Battle of the Marne could have imagined the war they were now fighting would go on to last another four years and kill millions of people.
But one thing became abundantly clear to both camps after one of the bloodiest battles in modern European history: despite the illusions commonly shared when they signed up to fight, they were not going to be home in time for Christmas.