Sure, but it's more a long-term benefit than an immediate exercise. Had you read it right now, what would you do make sure to get the most out of it? Would you sit down and write an essay about a related topic?

This question keeps bugging me. I know what to do about a programming or a self-development book, but humanities are much harder in that regard.

Why would I read it in the first place? That's the question you would have to answer to understand it.

Right now I'm reading Gibbon's Decline and Fall, and constantly stop to write down scenario ideas based on what he's describing. Of course, I also look up a lot of modern historical research on the matter — so I use recently acquired knowledge to understand related stuff and read about the same things from different sources. I also read comic books, having just finished the original Ghost in the Shell about 2 minutes before starting to write this comment; during the last week, I've set up animated-interactive-comic engine protorype in Unity3d and have been experimenting with primitive compositions that would work well both as game cameras and frozen comic panels.

If you want to read and remember something in the first place, you must have motivation. And creation and curiosity are the best kind.

Oh, and I know for a fact that I won't remember a lot of roman history a year later, and that's ok: I only want to remember staff that I actually find interesting.

I read it for the long term benefits - better command of the language, appreciation of the historical context, understandig human nature as described by the author, trained ability to focus on a long form (and thus a long, elaborate thought), a cultural context that I can refer to in a conversation.

There's a bit of a gap between the long term benefits and immediate actionable exercise.

Perhaps you are correct, and if I take each one of the benefits individually I can come up with an exercise that drives the point home. It seems like a daunting task though...