In 1941, in German-occupied Poland, the Nazis began abducting members of the Jewish population and imprisoning them in extermination camps.
But there were exceptions.
The Nazis held foreign passport holders in detention camps to be traded later for Germans detained abroad.
With this loophole in mind, Aleksander Ładoś, a Polish diplomat in Switzerland, started producing forged Latin American passports and smuggling them to Polish Jews.
In the end, these simple paper booklets would mean the difference between life and death for thousands.
A striking thing about passports is that they're actually a relatively new invention.
They're not the first form of travel documents.
In ancient Egypt, travelers carried letters of safe conduct issued by rulers.
In Han China and Tudor England, foreigners were issued travel passes.
And in the 19th century, poorer migrants often needed health certificates to enter the US.
