Game keeps crashing

I've logged almost 600 hours of Civ 5 without any major technical issues, but recently (not sure exactly when) it's started to consistently freeze up, at which point the only way to fix it has been to Ctrl+Alt+Delete out, which causes it to immediately close. It only does so part way through a game, generally around turn 200ish, and before it starts to crash the leader scenes often begin to glitch graphically with weird colours. There tend to be specific things that trigger the crashes, setting up a trade route is the most common cause but it's also happened in a few other situations like using a great scientist to advance to the next era, I tried the latter four times using autosaves and it always crashed at exactly the same point. I can work around it by not doing whatever caused the crash, but shortly afterwards something else starts crashing the game. In the great scientist game I ended up getting to the next era the normal way, which avoided that particular crash, but then a few turns later it began crashing whenever I sent a trade route. This makes the game mostly unplayable after I reach the point of repeated crashes.