lol i have similar Situation in my game.
I'm in the northernmost region of my continent. the the Se theres a huge bay which pushes inland, just 2 squars down a mountian chain that stretchs 6 or 7 squares, and to the West of the mountian chain is spain, and to the East is a spanish city. I managed to build 2 cities south of the mountians. Then Spain cut off their borders with me. there was a small ammount of territory that was unclaimed that i slid a few troops thru, I sent a settler to the terrirtory to ensure a connection so I could spread my religion to Greece, Rome, and Aztecs. Butt by the time my settler got there they expanded. Now I've been pushing as much culture as I can in the the 2 Cities I have on opposite sides of the moutnian chain, hoping to push them off, and Im primarly building settlers n troops in the other cities S of the Moutain Chain. I've successfully Cut the Egyptians off from their City on the Eastern end ofthe mountain Chain, and blocked them from the Aztecs, who both hate eachother, and both have cancele open borders with me. The only way the Egyptians would be to fight is to march thru Greece, and Greece dont like them, the Aztecs however, love the greeks, So the Egyptians wil lget screwed. Ofcourse, Once I convert Caesar, I feel that the Spanish will face my Wraith.
point is, there should be some kind of special worker u can build that takes 3 times longer to build, but can make a road over mountains. allowing troops to pass over it.