[humblegunner]

There are all kinds of limestone based architecture that have existed for more than a few hundred years.

Surely. Look at the pyramids.. awesome engineering.

You're just being difficult.

Is this dam natural or un-natural?

And I repeat.. quibbling over construction materials aside.

Why is a beaver dam natural and a human dam isn't?

A dam is a dam.

[UCANSEE2]

Is this dam natural or un-natural?

Uh-huh.

Why is a beaver dam natural and a human dam isn't?

They are both natural.

However, the beaver dam is made by randomly shoving cut logs down the river, hoping they will stay in place, until enough are piled there that they 'jam' together. (Many logs don't stay in place, and sometimes it doesn't work at all).

A human dam is not made randomly.