This is sort of where I disagree. Hindsight is 20/20 of course. But to me one major element letting down the defense is the line itself, by it's conception, contruction and the thinking it supported. The problem with the line can be best described in the following realisation IMO. A large part of the French army was encircled and pinned against the Maginot line in 1940. Had France tried to fight on they would have had something like 1/3 of the army cut off and strategically unsupported. From an already weaker starting position than the German one. Further it's problematic when we say it forced the Germans to go around, since that's what they planned to do anyway. So in a sense it didn't really force the Germans to do anything. What it however did very effectively was force the French into committing to very static defense. WW2 showed how inadequate fixed forifications were in a modern war usually are. Much of the German Blixtkrieg success came from their opponents insisting on playing ball with them. In the end trying to blixtkrieg they way out every problem turned the war on them.
Which is why I think the Maginot line did exactly the opposite of what it was supposed to do. Wikipedia lists a set of 9 things it was supposed to do, and it more or less completes 4-5 by my count. 2 of those would have happened anyway and none of the reasons were relevant within weeks of the attack of France. Basically the Maginot line is a result of and cause of France's inflexible military thinking, consuming most what little military resources existed in a way that was essentially doomed from the start.
I can't say France would have necessarily been better off without it, but at least not been worse off and may have given a military mindset more appropriate to modern war (e.g. defense in strategic depth).
In (pre) ironage Scandinavia "forts" built out of stones piled up on high hills and rocky outcrops existed close to most larger communities where people would flee to wait out hostiles. Presumably the towers themselves or similar fortifications would be built. The mediterranean coast in many places is ideal for it.
I'm not convinced you can really parcel out tactics from weapons, technology and society like that. Basically tactics are how you deploy the weapons and men at your disposal with regards to location, communications and how well trained they are. The last two are going dictate a lot of what you can do. You need well trained men to pull of feigned flights, various maneouvers in the face of the enemy etc. Being able to see and communicate with subordinates places heavy restrictions on what can be accmplished. Much of ancient and medieval tactics flows naturally from this. In a sense what I'm saying is that advanced tactics will have to be implemented when you train you first soldier. The best tacticians had well traine dmen and subordinates who knew what to do as situations unfolded with regards to the overall goal. E.g. Roman centurions .
Yup this. The limits of line of sight and ability-to-shout-loudlywas for the longest time hard limits on tactics.