During the First World War, British spies used semen as invisible ink.
Humans appeared 200,000 years ago. Written records begin 6,000 years ago. That means 97% of history is lost.
In medieval Baghdad, if you translated a book into Arabic, you'd be given that book's weight in gold.
The biggest genocide in human history didn't occur in Nazi Germany, but on American soil. 100 million native Americans were slaughtered and lost their homeland.
It has been calculated that in the last 3,500 years, there have only been 230 years of peace throughout the civilised world.
It is claimed that during the Battle of Stalingrad, more German soldiers died trying to unsuccessfully capture this one building from 25 Soviet soldiers and 10 civilians defending it than died in the entire invasion of Paris.
Genghis Khan was responsible for the deaths of so many people that the Earth's carbon levels dropped by almost 700 million tonnes.