After 100 years, read and watch why some WW1 trenches today are still uninhabitable on battlefields across Europe.

The most fought-over fort of the war was the Austro-Hungarian defensive system at Przemyśl. Begun in 1854, the network of defenses had been added to sporadically over the years, depending upon Austria-Hungary’s relations with Russia.

Some zones remain toxic a century later, and others are still littered with unexploded ordnance, closed off to the public. But across France and Belgium, significant battlefields and ruins were...

All over Northern France and Belgium, farmers and construction workers still regularly find remnants of the Great War, everything from unexploded artillery shells to rusted live hand grenades.

What exactly was it that made relatively modern concrete forts obsolete around WW1? For instance the Belgian forts around Liege were destroyed by the big bertha 420mm guns during the German invasion. But these forts were built in the 1890s, so they weren't Napoleonic vintage - they seem relatively new for the time to me.