Whenever I listen to the fortress town theme in HoMM3 the bit from about the 45 second mark onwards seems instantly familiar, but I can't place it. Any ideas, perhaps some blockbuster film?

Awesome theme though eh? Almost as good, or perhaps as good as the dungeon town theme.

One of the commenters on the vid you linked said "0:45 sounds like Prokofiev's 5th Symphony in Dm." . Maybe he's right ?

That symphony is 45 minutes long! Thankfully it seems only the 2nd movement is in D minor, and I can definitely hear the resemblance in parts.

It's not it though. I'm pretty sure I heard something like it in a film or game somewhere. Then again, I also used to listen a lot to Radio Rivendell, and sometimes they played music by composers such as Paul Houseman, and some of his stuff is in the same vein, though not in any games or films that I know of.

The music from that point on conjures up in my mind an image of a movie flyover. You know the type, where you're skimming along the ground, pass over a certain point (usually the edge of a cliff), and upon the screen opens a wide vista with some magnificent view of.... whatever. City, lush and verdant valley, coursing river and / or waterfall, something like that.

So that being the case, I've heard something like it in a hundred different movies.

That 0:45/0:46 mark and onward reminds me of one of the older Batman movies or some other action movie... HereForTheBeer is right. The violins in an escalating scale are used frequently in many movies and I could see it as a flyover.

First thing it reminded me of is the opening to Batman: The Animated Series.

Well, rising/falling Arpeggios are a very common thing in classical music and orchestral soundtracks, so there's roughly a million billion gajillion possibilities where you could have heard something similar.