I'm in Gibraltar, a bit of British territory on the south coast of Europe.
Over there is Spain,
and over there, visible on the horizon,
is the north coast of Africa.
In the 1920s,
a German architect named Herman Sörgel saw an opportunity right here.
He came up with a plan:
to drain the Mediterranean Sea.
It didn't seem entirely impossible.
The Mediterranean naturally evaporates:
more water comes in from the Atlantic than flows out,
so if you actually managed to put a dam across the Straits of Gibraltar,
the sea would slowly start to dry up.
Sörgel said that, after the sea level had dropped maybe 100 or 200 metres,
and a fifth of the water area had turned to land,
Europe and Africa would be united into one continent,
and there'd be huge amounts of new land for settlement and agriculture.
And you could use the dam as a massive hydro power station,
on a scale never considered before,
letting just enough water through to meet the energy needs of all of his new continent.
Sörgel made his plan public in the years after the First World War:
perhaps, he thought, all that new land and exploration
might be the solution to making sure there wasn't a Second.
The project was called Atlantropa,
and it is one of the most ambitious plans that has even been announced.
It would have taken an effort on the scale of the Apollo moon shot.
And it certainly got attention from the press and the public:
but there were a few slight problems with it.
First, there might not have been enough concrete in the world to build a dam that big,
let alone all the other secondary dams and earthworks elsewhere needed to make the project work.
And Sörgel didn't want the dam here,
where the Strait of Gibraltar is narrowest, no,
he wanted to build it about thirty kilometres that way, making it much, much longer.
It'd have needed to be 300 metres high,
and the foundations would be two and a half kilometres wide.
But those are practicalities, right?
Humanity could probably overcome that with enough effort and enough political will.
Not that there would have been enough political will:
the people on the Mediterranean coast would be, let's say,
rather disappointed that they now lived inland,
perhaps hundreds of miles from the sea.
Venice and Genoa, the folks there, were particularly unhappy with that.
The plan was popular in his native Germany but not particularly outside.
And as for Africa: well, it was the early 20th century,
their opinion apparently didn't matter.
It wasn't so much a merging of Europe and Africa as an attempt at assimilation.
But let's assume that, somehow, over decades,
the Atlantropa project was built.
There would have been some other problems.
All that new land would be salt flats,
completely unusable for growing crops or... well, for anything, really.
And although Sörgel couldn't have known it at the time,
some meteorologists now reckon that the project might have diverted the Gulf Stream,
sending temperatures plunging in most of Europe and ending local agriculture as we knew it.
And also, when Sörgel first came up with his grand plan,
there likely wasn't a bomb in the world large enough to destroy a dam that big.
Certainly not in one go, you could just about make it work...
but that changed quite quickly during the Second World War.
Having a single point of failure for millions of people's homes and lives is not ideal.
Sörgel died in 1952, and any hope of the project died with him,
after he'd spent a lifetime promoting it.
But his idea lives on in science fiction, and as a testament, perhaps,
not to how big we can actually build,
but just how big we can dream.