In one game ages ago, I had a continuous war with the Persians pretty much from when I met them until one of the other AI's eventually built the Spaceship.
In a true testament to dumb AI, the only way the Persians had to my territory was through a one-tile bottleneck, which as fortune would have it was a mountain. I had stacks of spearmen pileed high in my mountain fortress, defeating every single attempt to break through.
As the Romans, I thought, great! I'll have my legions marching towards Persiopolis in no time, but no. There is no iron, or horses, or ANYTHING.
This lasted all the way to the modern age, with either my spearmen or riflemen only just holding on against tanks due to sheer numbers. Luckily, no nukes were used. I was last in score buy a very very long way, and was at least TWO ages behind everyone in tech simply because all of my 6 cities where devoted entirely to churning out defenders. Things became much worse when Persia allied up with the other players on the continent, all of whom relentlessly attacked the fortress. It's a good job the AI can't understand bombardment!!!
I kept playing just to see how long I could hold on for, which in the end was until about 1980AD. How I wish there was a "Units Killed/Lost" stat on the score screen.... The game itself took over 30 hours, even with all animations off due to the about 20-30 attacks per turn.