Dr Adrian Goldsworthy

It's the only practical way.

The Persian Empire is very large, very strong, but it can't draw on that power quickly.

So a problem like this is something that if the king wants to muster an army from all over his empire, it's going to take a year or two.

to do that.

You can't just do it in months and then march it a long way.

It's like the old story of when the Spartans are asked to intervene, help the Ionian rebels, and they ask, well, how far away is Cephalus from the sea?

And at three months, oh yeah, we're not doing that.

Sorry, Garth, you can forget.

Again, it is vast.

It is huge.

It is very wealthy.

So it's got the organization, it's got the administration, it's got the manpower, but it can't mobilize that quickly.

So Darius doesn't have, unless he happened to be in Asia Minor,

There is no way that he's going to meet Alexander in that first year and no expectation.

This is the sort of problem your satraps can deal with.

Remember recent history.

Philip sent an advance guard.

They've pushed forward.

Quite a few local cities have defected to them or been conquered.

But in the sort of the lull when Philip's dead and Alexander's busy in Europe, they've been pushed back to a tiny enclave.