Wow! That is fantastic information! Thank you. I decided to get around the problem by using the actual thermopylae area (136-138x, 61-64y) which includes a v wide plain between the mountains and coast. I hoped one of the developers might have had the same urge and already included a nice Thermopylae area as an Easter egg. I settled on 138x and 62y and added a new bay reaching inland to form a choke point and extended a spur of hill to border it on the other side. This spur reached down to just the unplayable side of the infamous "red line" meaning it formed the other impassable barrier. This is not very satisfactory as it does not allow the all important flanking attack and i would have had to simulate the retreat of the greeks guarding it by bringing them on to the map as reinforcements followed in short order by the persians. It did allow a nice plain on either side for deployment however. Now, new possibilities are opened up.

I see someone else has had the same idea about this historical battle and ill post a link to this thread there. This is v. valuable information. Thank you once again.