I have always wondered why there never was a wall built roughly along where the Suez Canal now lies. I don't think it would have been that hard to build, there are other walls of that size built in the Roman era and I would think that it would have been possible before.
Now the question is would it work at keeping out invading hordes from the east, and the effects if it did.
Now the question is would it work at keeping out invading hordes from the east, and the effects if it did.