Helgen is on the frontier, closer to the border of another land, Falkreath is in a more geographically centered area.

What? Falkreath is much closer to the border. And a more hostile border at that.

But it's protected by nigh impassible mountains. The mountains to the S-SW of Falkreath offer no egress into Cyrodiil. So it doesn't matter where the map lines are drawn.

Impassable in the game. There are almost always passes in real, full-scale mountains. Falkreath had strong connections to Cyrod in the First Era, with a lot of Nords from there taking part in the wars with the Ayleids.

In the First Era. Much has changed since then.

I think that during the intro scene one of the guys in the cart comments on the "imperial walls", so they must be rather new. Perhaps the Nords in Falkreath never really saw a reason to have walls, and it wasn't until the Imperials came in that they were built.

The Imperials are there for nearly 600 years.

The mountains didn't. And no, two adjacent regions don't just stop having contact with each other.

You're saying that the Nords fought wars with the Ayleids, but once they were in the same state as Cyrodiil (for centuries and centuries) they started ignoring their neighbors? Emkay.

Please don't argue for the same of arguing, just because Falkreath is closer to the border than Helgen. It's not a plot hole that one has walls and the other doesn't.

Helgen is more accessible to the frontier, being it is on the road to another province. Travel south from Helgen past Fort Nuegard and you are in another province, well you are over the mountains that protect Falkreath. You have to go past Helgen to get to Falkreath if you were to invade, so it makes sense that Helgen is the fortified town.

Also, Helgen is closer to the border than Falkreath is. Not by much, but is closer as the crow flies. However, Falkreath is much farther away as the army marches.

http://images.wikia.com/elderscrolls/images/b/b7/SkyrimMap.jpg

This map makes Falkreath look closer, by a little bit. Not that it matters all that much. It also shows a road going over the mountains. The game doesn't show everything that is 'actually' there according to lore (or common sense, in this case).

It's a weird border to fortify in any case, as the Imperials would never build walls against Cyrodiil. Better to drop the whole line of reasoning. Much more likely is Falkreath losing the privilege to have walls, which historically speaking was a marker of independence.

This is the map I have been looking at for this discussion

http://www.gamebanshee.com/showshot.php?/skyrim/mapofskyrim/skyrimmap.png

Now, another thing to consider is the Imperials could have fortified Helgen when they were invading Skyrim as it was their beachhead or foothold so to speak. It was from there that they spread out to invade the rest of the province. That would explain the disdainful comment on the cart about the Imperial Walls. That is something that would grate on a revolutionary even 600 years after it happens.

Well this is awkward...

Alright here's an explanation, Falkreach, Dawnstar and Mothral were all nearlly annihilated during the Oblivion Crisis.

Another valid explanation. That would also tie in with my theory that they then took all the rubble they could salvage and used it to repair the more major of cities (Solitude, Windlem, Riften, etc.). I even gave the explanation that the ocean silt covered the ruins of Winterhold, but that's not even good enough for some of these people...

That's what I thought. If I was an Imperial, I would want a strong fort on the far side of the Pale Pass in the event of an invasion from the north. The walls could also have been built during the civil war to protect the Imperial garrison there or to ensure the border stayed open.

Hey, didn't Beth say we were supposed to see old Oblivion gates?

And it wouldn't have taken them more than a few man hours to add Oblivion Crisis ruins around all those old towns.