This is going to be the centrepiece of an upcoming campaign of mine.
I have a previous campaign (General Belisarius, ID#98) that has a scenario which makes you defend walls of a city. This scenario, as the title suggests, takes it one step further and features fighting in narrow streets as you desperately defend against a numerically superior Persian army.
This has a rather complicated trigger system, and despite about a week of play-testing, probably still has some errors.
Please email those errors, or any comments, criticism, and questions to firstname.lastname@example.org