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This tip is not more of a tip, but rather an interesting experiment which players can try to confound the attacking horde. For you to successfully pull this off, it is strongly suggested that you have a defensive army and are an experienced player.
One of my clan members gave me this idea, and I decided to try it out. The idea is simple and I feel like a fool that why could not I have thought this. You go for Forbidden City wonder, and build a Senate for that city … making it the Mega-Capital. Know that Forbidden City has a higher border push and being a wonder has oodles of hit points. You do this right, and put your capital wonder city right on the border of your kingdom and you suddenly have a veritable fortress city.
(Contribution from Ameya Mane) This will only work before the Industrial age, from then onwards normal cities have higher HPs!! Nevertheless, it could be a good military tactic to reduce capital timers.
There are a few drawbacks of this idea, first Forbidden City comes for a minimum of 250 Food, 250 Wood. Thus it cannot be your second city, also by this time you will have built a Senate. So while building your wonder, you will have to simultaneously raze your own Senate. If your Patriot dies during that time, then you will have to wait for the entire process to finish to get him back.