Since my own international travels really don’t date back that far — I was born in the 1970s and didn’t leave the country until the 1980s — much of how travel works today I take for granted as though it’s always been that way. for instance I had to get a passport for my first international trip beyond Mexico and Canada.

Growing up I would enter Mexico unaccosted, and return to the U.S. just showing my drivers license. As an 18 year old going to college in Southern California, Mexico was a place to drink legally. A mere government-issued ID no longer suffices for transborder traffic. So I certainly know that the rules of international travel do change. 9/11 saw to that.

However I had no idea just how recent the requirement of a passport for international travel really is, even though the concept of a passport is a very old one.

• The Latin phrase civis romanus sum or “I am a Roman citizen” was enough to travel across the vast Roman Empire unaccosted, because the retribution of Rome was known to be both fierce and certain if one of their citizens was harmed. That was the Roman passport.

• There were letters of transit dating back as far as 450 B.C. where a King would grant permission for travel and ask those to whom the letter was handed to assist in providing for safe passage.

• China had something closer to passports as far back as 200 B.C. during the Western Han dynasty where documents detailed personal attributes and granted rights of passage across Chinese territory.

• Only those who paid their taxes to the medieval Islamic Caliphate were granted passports – a receipt for taxes paid – which was a condition of travel across regions. The U.S. has recently started denying passports to those who owe taxes.

The first modern passport – using that term – dates to mid-16th century England. However passports weren’t commonly required for travel across Europe in the years leading up to World War I. Border agencies didn’t keep up with the volume of travelers that came with the advent of modern train travel. Rather than building up borders – or walls – passport requirements were relaxed. Indeed, where we now have passport-free travel across the Schengen area of Europe, that was also largely the state of affairs prior to the first World War.

When European governments began to erect border controls it was as much to keep skilled workers in as to keep foreigners out. That’s often the role that such agencies play. Recall which way traffic went over the Berlin Wall.

The U.N. held a travel conference in 1963 during which the abolition of passport requirements was discussed. It’s hard to imagine that passport free travel in much of the world was possible a century ago, and that returning to this was thinkable just 50 years ago. There’s something romantic about the notion of being able to travel anywhere and at any time, without permission, as long as you do not appear to pose a threat.. isn’t there? Of course discussions around that idea might as well have been 500 years ago, given how unlikely that is to come to pass again.