French President Francois and German President Joachim Gauck marked the 100th anniversary of the start of the First World War with ceremonies at Hartmannswillerkopf, a mountain peak in France's northeast region of Alsace.

Following the commemoration ceremonies — with flags honours and wreath laying — both presidents walked over the site of the future French-German Museum of the Great War.

They placed a message of peace in a time capsule, that was put inside the museum's foundation stone that they together set with cement. The museum is due to open in 2017.

A strategic control point over the Rhine valley, Hartmannswillerkopf or Vieil Armand — as it is known in French, saw some of the most intense battles of the First World War.

Within one year, the mountain peak was won and lost eight times. Armies at the time deemed its capture as strategically important and some 30,000 died fighting in the area. The cemetery contains the remains of 12,000 unidentified soldiers.

Hollande gave an impassioned speech to mark Germany's declaration of war on France on Aug. 3, 1914. He remembered the soldiers killed around Vieil Armand, but pointed out that France and Germany "who were regarded as hereditary enemies," reconciled.

He also appealed to the world to use Franco-German peace as a lesson in peacemaking and "to stop the suffering of the civilian population," in Gaza.