I recently have found a really fun thing you can do to other civs that share a penninsula with you. In the expansion era send a scout out to see what kind of land you are on. If you are on a penninsula and there is a relatively narrow section (1-4 tiles) between the penninsula and main continent (if there is one) you can easily stop your rivals from expanding beyond you by fortifying a spearman there. Easy, safe, and hilariously entertaining to see how easily you excel past your oponents...

-RC:egypt:

Yes! Just did this in a TD game - sent a scout to a narrow passage as you decribe - instant "Choke- hold" to the opponent. Some say this is "dastardly" but it is allowed. Usually even a scout is not harmed because in the early stages of the game the AI is not looking to war against us yet - then replace with spearmen as you did.

I was on a tiny map a few weeks ago and did this, limiting the Greeks to three citys.:D :D :D

It's possible to abuse this even on larger maps where the continents narrow. Even allies and friends can't pass units with zones of control like cavalry without getting shot at.