Okay, seriously: System specs please.
On what level did you set the graphics settings?
Are the drivers up to date?
My answer to your issue is the typical "update your graphics drivers etc." That is what you usually do when graphics issues appear. Of course, having in mind the numerous bugs of CiV, it is possible that you have a damaged save and that this issue will not be fixed unless you start a new game.
BTW, you are friends with Montezuma? I hate you for this
Graphics settings are on high.
Not sure what you mean by 'drivers'. If by graphics card, then it should be up to date.
I have an nVidia GeForce FX 5200.