How Do You Envision Middle-Earth?

[The Saucepan Man]

There seems to be a lack of typical medieval style fortifications in general.

Not sure that I altogether agree with you on this one, Bill. There seem to me to be fortifications where they are needed. So, Minas Tirith is fortified (and thus able to resist for some time attack by Sauron's forces). And I would imagine the other great cities of Gondor, such as Dol Amroth and (in it heyday) Osgiliath, to be similarly fortified.

The people of Rohan are slightly different. Being horse-lords, they are more nomadic in their origins and therefore would have less historic knowledge of fortification-building. And so they rely on Helm's Deep, originally built by Gondor and only strengthened by the people of Rohan. And there they go in times of trouble. They also have the option of withdrawing to Dunharrow, but that is more of a naturally occuring defensive position.

Hobbits and Bree-landers did not need great fortifications because they were rarely disturbed, and certainly not by great armies. Dwarves relied on the defensive adavantage bestowed by having their communities under mountains. Khazad-Dum and Erebor were fortified communities in a way, although (perhaps understandably) not built to withstand attack from the likes of Smaug and the Balrog. And as for Elves, well they seem to have relied largely on Elvish magic to protect their communities (Rivendell, Lothlorien).

So, having thought this through, it does seem that most of the "medeival-style" fortifications in 3rd Age ME were built by the Gondorians. Possibly because they were the only ones with the knowledge and the need to do so.