Same famous walls and lines and their effectivness

[TexasProgresive]

The failure of the Great Wall by Riho Laurisaar
http://gbtimes.com/life/failure-great-wall

How did it all work? Simple – the wall’s daunting appearance itself should have been enough to make possible invaders think twice about their intentions. Aside from this, there were also archers all along the wall, making it more of a threat. Unfortunately, invaders often decided to simply ride around the wall.

There were also large garrisons manning the wall’s larger gates, with the purpose of keeping invaders from breaking in. But again, unfortunately, during the most crucial stages of Chinese history traitors opened the gates for the enemy willingly.

The Great Wall served well in the times of the first emperor, as all invaders were effectively kept out of the country. However, one might argue that it was more due to Qin Shi Huang’s great armies and their achievements on the battlefield, rather than the effectiveness of the wall.

Rulers of the Han Dynasty hoped that the wall would offer them the same protection that it had for the first emperor, but this was not to be. The Xiongnu up north grew even stronger and in 200 BCE overran China, looting and plundering.

Hadrian's Wall: A Study in Function by Mylinh Van Pham San Jose State University
(This is from her conclusion. If you want to read the whole theses GOOGLE the title.)
For instance, the defense theory is not structurally sound because of the
number of openings along the Wall and how easily it was scaled. If we consider
the Wall was built around the Carvetii, a possible hostile, anti-Roman sub-group
of the Brigantes, the Wall was not used to keep the enemy out, but rather to keep
them in. Not much can be said against trade, except that we are unsure if there
were materials exchanged north of the Wall. There were definitely resources
being exchanged along the entire Wall. If trade and defense were the sole
important functions of the Wall, there would not have been much reason to make
the Wall aesthetically appealing by limewashing and rendering it, which gave it a
shiny look from afar.

To make the argument that Hadrian’s Wall was used for one specific
purpose is almost impossible because of the lack of evidence to support one
purpose and at the same time the amount of evidence against that same
purpose. Different parts of Hadrian’s Wall exhibited all three elements of
functionality, and it is difficult to pinpoint the exact purpose. The Wall probably
did not have just one specific function, but served many functions. The most
likely theory is that the Wall was probably constructed for defense, but then its
uses evolved into other purposes. It would not be correct to say the Wall was
only used as a defensive structure because there were so many gates and
98
openings and some ramparts were not big enough for soldiers to stand on. Trade
along the Wall is probable, but lack of definitive items north of the Wall presents
questions in this theory. Although Hadrian was a man of the arts and was
interested in architecture, it is unlikely that he would have this Wall and other
walls around the empire built solely as a symbolic gesture. In the end, one
cannot determine the sole purpose of the Wall because we can find sources to
support and refute each theory. This investigation strongly suggests that the Wall
served as a multifunctional structure.

Why France's World War II defense failed so miserably by Pierre Bienaimé
http://www.businessinsider.com/the-story-of-the-maginot-line-2015-4
The problem was that Maginot Line, a great line of fortifications that spanned France's borders with several neighbors, was essentially a glorified trench.

And like any trench, it belonged to the age of the First World War, not the mechanized warfare known as blitzkrieg that Hitler brought to the Second.

The Wehrmacht simply went around the line, borrowing the low plains of Belgium to France's north.

The line's fortifications were built to various degrees. The dotted lines across from Belgium and Switzerland in this map designate "rural fortifications."

[The Velveteen Ocelot]

1. Something there is that doesn't love a wall.

Before I built a wall I'd ask to know
What I was walling in or walling out,
And to whom I was like to give offence.
Something there is that doesn't love a wall,
That wants it down!

[TexasProgresive]

3. Robert Frost would heave border walls

That sends the frozen-ground-swell under it, (frost heave)
And spills the upper boulders in the sun;
(on the neighbor)
He moves in darkness as it seems to me,
Not of woods only and the shade of trees.
He will not go behind his father’s saying,
And he likes having thought of it so well
He says again, ‘Good fences make good neighbors.'

[Historic NY]

2. Only wall that seems to work is a

cemetery wall, its keeps its occupants in for eternity.

[TexasProgresive]

4. Years ago my boys and some friends mowed a couple of rural cemeteries.

One had a fence dividing it which was a real pain. My sons asked their friends why the fence? The answer, "to separate the whites from the blacks." My boys had to pick themselves off the ground where they lay laughing.

[braddy]

5. Those all fell to armies, not foreign civilians without passports, we need a better argument.

[TexasProgresive]

6. If they won't work against armies and hordes of barbarians they won't stop individuals.

[braddy]

8. LOL, if it can't stop the German war machine or Genghis Khan's army it can't make it easier to

control undocumented immigration? I think we need a better argument than that.

I think the public would say that if it isn't a hindrance to undocumented immigration, then we shouldn't be complaining so much.

[Hugin]

7. Don't forget "Offa's Dyke".

"Offa's Dyke (Welsh: Clawdd Offa) is a large linear earthwork that roughly follows the current border between England and Wales. The structure is named after Offa, the Anglo-Saxon king of Mercia from AD 757 until 796, who is traditionally believed to have ordered its construction."

https://en.wikipedia.org/wiki/Offa's_Dyke