Garrison for the Rammas Echor

[Kuruharan]

I think that the Rammas was partly symbolic

I agree with you there.

Had the Rammas not existed then small parties of orcs could have been constantly raiding the farms, burning crops and playing havoc with the city's food supply (as well as lowering morale) for years before the War of the Ring.

This is also true, but I don't think the wall was the correct tactical or strategic answer to these problems. I think Gordis is more on the money.

I think Tolkien may also have been inspired by real life fortifications - the Great Wall of China (which is thousands of miles long), Hadrian's Wall - and in the twentieth century The Maginot Line which was supposed to protect France from invasion by Germany.

Possibly...although its almost inevitable that somebody point out that none of those worked out very well.