A restoration expert collects medieval bone remains in an effort to preserve the Sedlec Ossuary in Kutna Hora, Czech Republic, February 14, 2019. Picture taken February 14, 2019. REUTERS/David W Cerny

Visitors observe the Sedlec Ossuary in Kutna Hora, Czech Republic, February 14, 2019. Picture taken February 14, 2019. REUTERS/David W Cerny

A restoration expert walks through the Sedlec Ossuary in Kutna Hora, Czech Republic, February 14, 2019. Picture taken February 14, 2019. REUTERS/David W Cerny

Visitors observe medieval human skulls at the Sedlec Ossuary in Kutna Hora, Czech Republic, February 14, 2019. Picture taken February 14, 2019. REUTERS/David W Cerny

Medieval human skulls and bones are piled up at the Sedlec Ossuary in Kutna Hora, Czech Republic, February 14, 2019. Picture taken February 14, 2019. REUTERS/David W Cerny

Medieval human skulls and bones are piled up at the Sedlec Ossuary in Kutna Hora, Czech Republic, February 14, 2019. Picture taken February 14, 2019. REUTERS/David W Cerny

Medieval human skulls and bones are piled up at the Sedlec Ossuary in Kutna Hora, Czech Republic, February 14, 2019. Picture taken February 14, 2019. REUTERS/David W Cerny

A restoration expert collects medieval bone remains in an effort to preserve the Sedlec Ossuary in Kutna Hora, Czech Republic, February 14, 2019. Picture taken February 14, 2019. REUTERS/David W Cerny

Medieval human skulls and bones are piled up at the Sedlec Ossuary in Kutna Hora, Czech Republic, February 14, 2019. Picture taken February 14, 2019. REUTERS/David W Cerny

A restoration expert collects medieval bone remains in an effort to preserve the Sedlec Ossuary in Kutna Hora, Czech Republic, February 19, 2019. Picture taken February 19, 2019. REUTERS/David W Cerny

A restoration expert collects medieval bone remains in an effort to preserve the Sedlec Ossuary in Kutna Hora, Czech Republic, February 14, 2019. Picture taken February 14, 2019. REUTERS/David W Cerny

An archaeologist collects human bones as part of a restoration work in an effort to preserve the Sedlec Ossuary in Kutna Hora, Czech Republic, February 14, 2019. Picture taken February 14, 2019. REUTERS/David W Cerny

A restoration expert collects medieval bone remains in an effort to preserve the Sedlec Ossuary in Kutna Hora, Czech Republic, February 19, 2019. Picture taken February 19, 2019. REUTERS/David W Cerny

A restoration expert sorts medieval bone remains in an effort to preserve the Sedlec Ossuary in Kutna Hora, Czech Republic, February 19, 2019. Picture taken February 19, 2019. REUTERS/David W Cerny

A restoration expert carries a box containing medieval bone remains at the Sedlec Ossuary in Kutna Hora, Czech Republic, February 19, 2019. Picture taken February 19, 2019. REUTERS/David W Cerny

A restoration expert sorts medieval bone remains in an effort to preserve the Sedlec Ossuary in Kutna Hora, Czech Republic, February 19, 2019. Picture taken February 19, 2019. REUTERS/David W Cerny

A woman walks among the tombstones at the cemetery outside the WWI Douaumont ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, near Verdun, France, November 7, 2018. REUTERS/Christian Hartmann

A woman walks among the tombstones at the cemetery outside the WWI Douaumont ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, near Verdun, France, November 7, 2018. REUTERS/Christian Hartmann

A woman walks among the tombstones at the cemetery outside the WWI Douaumont ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, near Verdun, France, November 7, 2018. REUTERS/Christian Hartmann

A French soldier's tombstone is seen in the early morning light at the cemetery outside the WWI Douaumont ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, near Verdun, France, November 7, 2018. REUTERS/Christian Hartmann

French soldiers tombstones are seen in the early morning light at the cemetery outside the WWI Douaumont ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, near Verdun, France, November 7, 2018. REUTERS/Christian Hartmann

French soldiers tombstones are seen in the early morning light at the cemetery outside the WWI Douaumont ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, near Verdun, France, November 7, 2018. REUTERS/Christian Hartmann

French soldiers tombstones are seen in the early morning light at the cemetery outside the WWI Douaumont Ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, near Verdun, France, November 7, 2018. REUTERS/Christian Hartmann

French soldiers tombstones are seen in the early morning light at the cemetery outside the WWI Douaumont ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, near Verdun, France, November 7, 2018. REUTERS/Christian Hartmann

French soldiers tombstones are seen in the early morning light at the cemetery outside the WWI Douaumont Ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, near Verdun, France, November 7, 2018. REUTERS/Christian Hartmann

French soldiers tombstones are seen in the early morning light at the cemetery outside the WWI Douaumont Ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, near Verdun, France, November 7, 2018. REUTERS/Christian Hartmann

French soldiers tombstones are seen in the early morning light at the cemetery outside the WWI Douaumont Ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, near Verdun, France, November 7, 2018. REUTERS/Christian Hartmann

French soldiers tombstones are seen in the early morning light at the cemetery outside the WWI Douaumont Ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, near Verdun, France, November 7, 2018. REUTERS/Christian Hartmann

French soldiers tombstones are seen in the early morning light at the cemetery outside the WWI Douaumont Ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, near Verdun, France, November 7, 2018. REUTERS/Christian Hartmann

French soldiers tombstones are seen in the early morning light at the cemetery outside the WWI Douaumont ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, near Verdun, France, November 7, 2018. REUTERS/Christian Hartmann

Barbed wire is seen near the grave of an unknown French soldier at the "Tranchee des Baillonettes" (Trench of Bayonets) monument of Douaumont near the WWI Douaumont ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, in Verdun, France, November 5, 2018. Picture taken November 5, 2018. REUTERS/Christian Hartmann

A man walks among the tombstones at the cemetery outside the WWI Douaumont Ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, near Verdun, France, November 5, 2018. Picture taken November 5, 2018. REUTERS/Christian Hartmann

A man walks among the tombstones at the cemetery outside the WWI Douaumont Ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, near Verdun, France, November 5, 2018. Picture taken November 5, 2018. REUTERS/Christian Hartmann

The grave of an unknown French soldier is seen at the "Tranchee des Baillonettes" (Trench of Bayonets) monument of Douaumont near the WWI Douaumont ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, in Verdun, France, November 5, 2018. Picture taken November 5, 2018. REUTERS/Christian Hartmann

The grave of an unknown French soldier is seen at the "Tranchee des Baillonettes" (Trench of Bayonets) monument of Douaumont near the WWI Douaumont ossuary, as France prepares to mark the centenial commemoration of the First World War Armistice Day, in Verdun, France, November 5, 2018. Picture taken November 5, 2018. REUTERS/Christian Hartmann

French President Emmanuel Macron walks at the cemetery by the Ossuary of Douaumont during ceremonies marking the centenary of World War I, near Verdun, France November 6, 2018. Francois Mori/Pool via REUTERS

French President Emmanuel Macron is flanked by students as he pays his respects at the Douaumont Ossuary, in Douaumont, France November 6, 2018. Ludovic Marin/Pool via REUTERS

French President Emmanuel Macron is flanked by students as he pays his respects at the Douaumont Ossuary, in Douaumont, France November 6, 2018. Ludovic Marin/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron walk with French Junior Minister for Defence Genevieve Darrieussecq (R) and French Junior Minister to the Minister of Territorial Cohesion and Relations with Territorial Communities, in charge of territorial communities Sebastien Lecornu (back) at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron walk with officials and students at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron walk with officials and students at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron talk with students as they walk at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron talk with students as they walk at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron walk with officials and students at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron walk with officials and students at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron walk with officials and students at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron walk with officials and students at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron walk with officials and students at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron walk with officials and students at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron walk with officials and students at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron walk with officials and students at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron walk with officials and students at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron walks with French Junior Minister for Defence Genevieve Darrieussecq (R) at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron walks with French Junior Minister for Defence Genevieve Darrieussecq at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron walk with officials at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron walk with officials at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron walk with officials at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron walks with French Junior Minister for Defence Genevieve Darrieussecq (R) to the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron and his wife Brigitte Macron walk with officials at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS

French president Emmanuel Macron walks at the Douaumont National Necropolis and Ossuary during ceremonies marking the centenary of the First World War, near Verdun, France November 6, 2018. Etienne Laurent/Pool via REUTERS