You join me today in ancient Greece.
It's- - (Well- this)
(doesn't look like it. They've good lighting.)
Thanks, it's it's not not what you were
expecting but it's 6th century BC
and in particular we're on a Greek
island just off the coast of Turkey. It's
called Samos and,
I know what you're thinking, you'd like
to dig a tunnel through a mountain,
wouldn't you?
Question is how on Earth do you dig a
tunnel through a mountain when you don't
have access to any modern equipment?
I'll tell you how you dig a tunnel
through a mountain! Okay so here is your
mountain,
lovely. Now there are a couple of things
that you need to dig a tunnel through a
mountain: you're going to need to have an
entrance and an exit, those are
the two requisite components of a tunnel.
So let's say you want to go in here
and you want to come out here.
Now the thing is is that you can't just
start digging in here and just
hope that you'll come out here, it's not
gonna work right? You need to make sure
that you hit the right bit. So what
people tend to do - this is what they did
for the channel tunnel for example -
is you start digging here and you start
digging here and you just hope that they
line up.
Except that- I mean- you you're
unlikely to find each other in the
middle of a mountain.
So you need a technique to make sure
that these two lines end up meeting up
in the middle. And the way that you do
that is by using triangles.
(I would have thought if you made)
(absolutely sure you were digging in a)
(straight line)
(you'd be all right.)
(As long as you can always- as long as you)
(look behind you and the hole)
(is still behind you- ) - Yeah but the
straight line- Hang on, if you were in a
straight line, okay so let's imagine that
you- let me do like a contour of this
mountain.
It's quite a wobbly mountain this one. So
you want to go in here and you want to
come out here; the problem is that if you
dig in a straight line you could end up
over here.
(Right, so how do you make sure- ) - How do you make
sure that you get exactly there?
And it's not like you can just stand on
the top of the mountain and you go,
heading that way lads.
You know what I mean? Because you can't-
when you're standing over here you can't
see around there. - (Right)
So it's really hard to even- to even know. (I feel like in)
(the era of GPS you could just do the)
(straight line.) - In GPS I think you
probably can. I think you probably can.
Apart from the fact that you're in a
tunnel, I don't think signal's great in
tunnels but-
(If you start in a straight line and then)
(just keep looking behind you to make)
(sure that the hole's still there, you)
(know you're going in a straight line.)
(Anyway.)
(So you're saying the main problem is you)
(can't see the other side?) - You can't see
where you're going, yeah, exactly.
So the way that you do this,
it's very neat.
So you try and walk around from one side
of the mountain to the other, and as you
go - you want to try and stay at the same
level as you go around - every time you
take a step south you add it up, every
time you take a step to the
west you add up, and you're very careful
about how big all of your steps are as
you're going.
Maybe you do this twice just to make
sure you've got the right numbers. You've
done it all in units and right angles
and you've been really careful all the
way along; because even in ancient Greece
you can imagine it'd be quite easy to
construct a right angle, wouldn't be too
difficult. But in total then, imagine that
you have taken 84 steps west and you
have taken 13 steps south. So effectively
then to get the direction from one place
to the other you are talking about a
triangle
with those as the sides, so you know it's
going to be 84 along there and 13 along
there, and you know that that's a right
angle because you've only ever walked
south and west. And so you have this very
nice neat triangle - I deliberately chose
one that was a Pythagorean triple, you're
welcome - so this is 85.
So now actually when you are at the
entrance to each of these tunnels
you can construct a much smaller version
of the same triangle and build it here.
And if you make a kind of really long
rod to sort of extend that angle, and you
do the same thing over here so you've
got another version of the triangle here,
then you should have
these two lines- these two angles that
will meet really perfectly in the middle.
So the only thing you've got to be
careful of now
is when you're digging
to make sure that you stay perfectly
flat, you don't want to go up you don't
want to go down.
And the way that they do that is that
they put water in the tunnel,
and then as they're digging they make
sure that the water just sits nice and
still rather than dripping in one
direction or the other. - (Like a spirit level?)
Like a spirit level, exactly. This
particular mountain, this is Samos and
this was in 525 BC.
Polycrates - I don't think he's called
Polycrates-
'How do you pronounce Poly-crates?'
[Computer: Poly-crit-ees]
Oh it's Polycrates- whatever, Polycrates
he wanted a tunnel.
You can- you can shush. Polycrates he
wanted this tunnel; it's a kilometer long,
525 BC this was built and this is exactly
the technique that archaeologists think
that they used.
And when they did so they did incredibly
well. There was a tiny bit of zigzagging
at one end, and they think it was because
they were trying to work their way
around some quite difficult rock, but
then they re-established this sort of
plum line as it were. And when these two
tunnels met in the middle, there's like a tiny
little step of 60 centimeters. It's like
this unbelievably remarkable achievement
with just some triangles.
(How do you know where to put those)
(triangles so the triangles are at the)
(right-) - That's got to be a line that runs
exactly
east to west, and that's got to be a line
that runs exactly north to south.
Do they have compasses?
I'm assuming they had compasses. - (Well)
(they knew- they had the sun.) - They had the
sun yeah, yeah that's true. Your
open and close to the tunnel, they
actually need to be at the same level
before you start. You know the water-
(At the same altitude?) - Yeah the same altitude, exactly.
Your water thing wouldn't work if you
had one of your- if you're like yeah yeah
let's start there and you hadn't worked
out that actually one was much more
uphill than the other. Now this is
something they're not quite sure about
how they did it, how they managed it, but
there is some suggestion - I think it's
I'm not convinced by this - but there's
some suggestions some archaeologists
think that created this tower and then
got a massive long stick.
I mean,
maybe I haven't understood this quite
right, but my understanding of it is they
went up to the top of the tower and then
they dangled a big long stick down and
then they sort of swung it around the
mountain. So they were like, oh there you
go, that's a nice point right there.
(Well you could use a rope for that surely)
And make it straight? Yeah. - (Like taut,)
(although it's pretty hard to keep a rope)
(that long taut.) - Yeah it's like a
kilometer.
But I don't think they built a kilometer
long stick either.
Anyway, some mysteries remain unsolved
shall we say.
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