Age of Empires III - Guard Towers Are Go!
I wish I could build more guard towers.
In Age of Empires II you could build as many guard towers as you wanted. You could build 1 or you could build 50. Instead of building a stone wall around your town, you could build a guard tower wall - that's how many guard towers you could build. Not so in Age of Empires III.
They've limited the amount you can make in AoE III and I get why - it's just annoying. Luckily, the French have some sort of a guard tower fetish and I've managed to upgrade my town to be able to hold more at a time. I'm sure the other countries have access to this upgrade but, for the sake of the French, I'm not even going to look. I'm just going to say that they don't. The French need a break, am I right?
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If I had one regret in life, it's that I've never learned how to properly utilize guard towers (much less build) in my own life. I've had dreams of it - I've dreamt of building them around my car when I park in seedy areas so as to ward off iPod stealers. The best part about guard towers is that they don't have to be manned - they automatically fire at strangers. The only problem with this is that people with other cars to get to (and their cars) would be decimated on first sight (even strange buildings* get fired at).
*NEVER take candy from a barracks stranger - not even if they say they know your town center.