*suggest sticky*
The rush is a very tricky thing. It can be easily countered if you know it's coming. Here are some signs and what to do when you see them.
How to Spot a Rush
Send your scout directly to your enemy city the FIRST thing you do (maybe after you start caravan/city district building).
If he's vinci and he's got 2 industrial districts he WILL be rushing with sniper/spider at about 3 minutes.
If he's any other race and he has a military district in his first 2 districts he will most likely be rushing, prepare to counter it.
If he's cuotl and he has a holy district in his first 2 districts he might be rushing using the holy arc to heal his units/avoid attrition
If he has a merchant district as his first district there's a good chance he won't be rushing until at least 5 minutes (preparing a 150 rush posibly). He might raid before that, but he won't rush full out until he fills up that 150 econ.
If he's got 2 merchant districts, he's almost certainly not rushing (unless he's an idiot).
What to do about a rush
Now, you SHOULD be able to scout your opponent BEFORE you start building your 2nd district. If you send your scout to them right away you can see both their first district and what their 2nd district is building right about the same time your first district finishes.
With this in mind, if you feel you MIGHT be rushed, consider building a military district as your 2nd district. Not only will this provide free units, it will make your city almost imposible to capture with teir 1 units in a rush situation. It boosts the attack of the city from 1 to 7 and increase hitpoints by 500+ i think.
If you wait to build a military district until your 3rd, he might be able to attack you before it finishes. If that happens and he knows what he's doing, that military district will never be completed. So it's a trade off between building a military before merch/whatever and having that extra protection. But if you think he could be rushing DEFINATELY build a military as 3rd district as insurance.
If he is Alin and you see a military and magus district as the first 2 then he probably has a circle somewhere just outside your territory. The most likely place is your first likey capturable city, he will plan to attack your units as you get this city. As soon as you realize he has magus+military scout all around your boarders and find this circle. Circles fall like paper so it will be very easy to destroy before he gets enough units to finish the rush.
BUILD A HERO! I can't stress this enough. If your opp is rushing a HERO really ruins his day. You definately want a walking hero so you can trample his masses of infantry (as that is almost always the only thing a rusher has except for vinci clockwork rush).
BUILD A BARRACKS! Build a barracks in an out of the way place (behind city is a good place) if you think they will be rushing. This is important because you want your barracks protected at all costs to keep units pumping into the battle.
If he attacks your mines just have your miners run toward your city and hit his units with focus fire. Your miners can usually last a good bit and taking down his units (while they do nothing to yours) is much mroe important than the 30 seconds of lost timonium income. As soon as you've pretty much crushed his army just send the miners back in and continue to expand.
Use your city! As mentioned before, the city has a lot of attack (reletive to teir 1) when you get your military district up. Always pull the fight back to your city so he's taking extra damage!
Continuously build units and keep them coming into the fight!
Scout, Scout, and Scout! Just keep your scout moving around likely attack routes and find his army before he attacks, it's very helpful!What Units to Build
Vinci - Clockwork men and Muskteers. Spend all your wealth (after you've queued up a hero) on CWM and build muskets with all timonium during the battle. Also if you have a military district already put in a industrial next and pick the next unit (sniper or spider) to help hold off the rush.Alin - Most make the mistake of building a sand circle first to counter the rush. You want a fire circle becaue you want SALAMANDERS! These are your anti-rush units. Not only do they do splash damage so they can hold off infantry very well, they do a peircing attcak (90% damage vs. medium, 80% vs. large) which is still pretty effective against medium and large units (clockwork units and heros!). Your basic desert walkers get destroyed by CWM because they have a skilled attack (75% damage to CWM, only 50% damage to heros). Also, the alin get lots of free desert walkers, so for the first part of the rush you should have plenty. If you build a military district and researched evocation you DEFINATELY have plenty. Build a sand circle after you get fire and queue up a salamander.
Cuotl - Again, the higher teir unit is better. Your opponent will almost always be coming with lots of cheap infantry, so getting some early jaguars is really great to stop this. Regular sentinals are good too, and since they sort of cost oposites, build both, but prioritize jagauars if you can (lots of reactor districts!With these steps in mind you should be able to crush any rush unless their micro is much better than yours (in which case, you probably shouldn't be playing them, lets hope more people come in so the system is better for newbies!).