[lifeisstillgood]

Well 20 miles from a navigable river looks a lot like most of populated Europe and China...

But I absolutely take the point - anything that can fit in an online comment is a gross simplification- especially for "farming since invention of agriculture".

Also the 20 mile is not a hard limit - it's easy to envisage some kind of system where I grow my cash crops near transport like river or coast, and sell them on a trade network, and you grow different crops further out and bring them not to the river / coast but to me to feed me. That probably will be more efficient but just look at the network of trust and possible disasters required - only very stable politics would allow anything like that - and that stability was rare. China probably had more of that for more of the past 2000 years than anywhere else - and that may be the cause of the invention of the bureaucrat!

[thrown_22]

Navigable for a barge and navigable for a canoe are two very different things.

The Danube and the Rhine were the two major rivers that could be navigated by Romans and they were the borders of the empire for that reason: they were the only way to supply border garrisons efficiently. They also had the Nile which isn't _in_ Egypt, but _is_ Egypt.

China by comparison is three major rivers which change course frequently and violently: https://www.youtube.com/watch?v=QFsQoY32n5g

[Someone]

> The Danube and the Rhine were the two major rivers that could be navigated by Romans and they were the borders of the empire for that reason: they were the only way to supply border garrisons efficiently

I don’t see why the southern shore of the river would be easier to keep supplied from those rivers than the northern one. So, if the empire ended there because of supply issues, wouldn’t it end a short distance north of the river?

Also, wouldn’t those rivers only help supply from other border areas, not from the much larger inner parts of the empire?

I would think those rivers just are natural boundaries because they provide some protection against invading enemies.

[thrown_22]

>I don’t see why the southern shore of the river would be easier to keep supplied from those rivers than the northern one. So, if the empire ended there because of supply issues, wouldn’t it end a short distance north of the river?

Retreat is easier when not drowning.