Er, one, it is really cold here and I want to move on,

but also because I didn't know I was going to be passing through Schengen,

a little town in Luxembourg on the borders with France and Germany, until today.

But here I am, next to the international border, the Moselle River,

and that border is a little bit weird.

And I wasn't going to do another video about a weird border. Because I've done that.

Years ago I went to the towns of Baarle-Nassau and Baarle-Hertog

in Belgium and the Netherlands,

where the borders are incredibly complicated and twisted thanks to history.

But that's an old video that I'm not really proud of,

and frankly it's not that interesting:

I only managed about a minute of script

before I had to go into a diversion on sovereignty

and why we even have borders in the first place.

Strange borders often make for great video titles,

but there's not much to talk about other than “huh, that's weird”.

Which is also why I've never been to the island that changes country every six months

between France and Spain.

Because once you're there, what is there to say but, “huh, that's weird”.

But it turns out this border raises a different question.

If you look on the map, there is a tripoint just of there, to the west of an island:

that's where France, Germany and Luxembourg all meet.

It was here – actually, on a boat out at that tripoint,

where the Schengen agreement was signed,

where most of the countries of the EU, all the ones that have their flags here,

decided to open their internal borders.

But that the tripoint there is not strictly true.

The border between Germany and Luxembourg doesn't follow the Moselle river:

the border is the Moselle river.

And that's an important distinction.

In most cases, international borders that follow rivers

are defined as following the centre line,

which raises questions in itself,

because rivers can erode the banks and change paths sometimes,

but borders are, at least, usually defined as a line of theoretically zero width.

Which is how mapmakers mark it.

But here, Germany and Luxembourg share the river north of France. It is a "condominium".

Under the treaties they signed, they both have full control over it.

Which means that if you're standing on the north tip of that island,

or on that bridge up there,

you are in both countries at the same time.

Not just in terms of having a foot on each side,

although that may well be how the locals treat it,

and that's certainly how the signs mark it.

But no: standing on that bridge above the water,

all of you is in both countries simultaneously.

This international border is a shape, not a line. It's two-dimensional.

Although, actually, I guess it's three-dimensional if you count depth.

Half an hour of research, and I can't tell you why they made that decision,

or what the legal result would be if you tried to commit a crime

on that bridge or on a boat on the river.

I even asked the folks at the little European museum just over there,

and they didn't know the answer.

Although they do have a lovely little display of all the border guard hats

that the Schengen agreement made obsolete.

I suspect that the answer would be “treat it as if it's a line, it's easier”.

And that's what I mean when I say that there's not much to talk about here.

Because that's one of the wonderful things about borders like this:

when you can walk between three countries

as easily as you can walk between counties or towns or neighbourhoods:

it's a lot easier to say “huh, that's weird”

and just get on with your life.