I have exactly the same problem and it has only got worse 
Used to be I could rely on getting to the Renaissance before it started tripping, now even on the lowest graphics settings and a 'normal' size map it seems to happen without fail while I am still in the ancient / classical age. Needless to say, it's not worth playing BTS till this is fixed.
Could be hardware I suppose, but it only happens when BTS is running.

Used to be I could rely on getting to the Renaissance before it started tripping, now even on the lowest graphics settings and a 'normal' size map it seems to happen without fail while I am still in the ancient / classical age. Needless to say, it's not worth playing BTS till this is fixed.Could be hardware I suppose, but it only happens when BTS is running.
Seems odd, though, that I can run things like Silent Hunter 4 on it, albeit slowly, without it giving up.

but gives no more information that is useful for anyone outside the developer - you might want to contact take2 with this 