Talk of big fences between the U.S. and Mexico has had me wondering when someone would mention this ... from an Op-Ed piece in the Star-Telegram:

So, Congress, some of you want to build a 1,951-mile wall to close off America's southern border?

Interesting, but not original.

As the people who'd be footing the bill, we have one request: Consider any of these examples -- none of which stopped those who really wanted to cross into a country from doing so -- before you consider spending taxpayers' money on such folly.

100s: Roman Emperor Hadrian orders construction of a wall in northern England to mark the boundary of his empire -- and keep the barbarians to the north at bay.

[more, later exempla follow] Not sure it's a fair comparison ... or are 'invasion' and 'immigration' (albeit illegal) the same thing?