I am taking the last few posts as a hint that I have add more military strategy content to further the discussions. However, beware I do have strong opinions on this subject. If you are easily offended by someone who does not share your views then do not read further. I am letting it all loose.
I will fist talk about the military units their best roles and key upgrades to look out for.
Slingers
Main Roles
1) They help you boost archery.
2) They upgrade to archers
3) They also may help you with some early barbarians too, but the above 2 goals are far more important.
Promotion Suggestions
Unless you are desperate and need to defend your city or encampment always go down the following upgrade path
Volley -> Arrow Storm -> Emplacement -> Expert Marksman path.
If you Choose Garrison as first upgrade you should probably always go down the right side to Expert Marksman.
However if your chosen upgrades are Volley, Arrow Storm and Garrison, then it will be a deadly defender unit.
If you have a city or encampment on border of a enemy city though they can become a dangerous offensive unit as well.
Expert Marksman is probably the most powerful upgrade of all. If you get your unit to this upgrade they can change the tide of a battle. Make sure to use them well.
Archers
Main Roles
1) They are your primary attack power until horseman or swordsman. By primary attack power I mean they usually go in first and kill everything.
2) They weaken Cities so a melee (ex. warrior) can take over after hitting it once more.
3) Help you deal with barbarians
Upgrades Suggestions (read slinger upgrade section)
Strategies
1) Hit and Run.
2) Hit, Hit and Hit enemy some more.
3) Taking hills tiles to hit enemy archers on forrest tiles. All archers cannot shoot through forrests or hill that are two tiles away unless they are on a hill tiles. If you have the higher ground you can get 2 shots on enemy archers before they could get close enough to return fire.
4) Building a city or encampment near enemy territories then putting an archer in with Volley, Arrow Storm and Garrison promotions. Can attack city and units around near enemy city with greater damage capabilities.
Warrior
Main Roles
1) They help you deal with early barbarians encampments
2) They capture weakened cities (that archer units have damaged first)
3) They upgrade to swordsman
Strategies
1) Avoid confronting a group of archers with warriors. A group of archers just have an advantage over warriors.
2) Let archers deal with the any military units and city defense. Then let a warrior move in for final blow
3) Try not to let warriors die needlessly. They each have the potential to become a power swordsman (more on this latter).
Promotion Suggestions
I used to always go with Battlecry first, but I believe that was a newbe mistake. A lot of people on multiplayer use archers as their main offensive 2-3 shots can easily kill a warrior. That is why I recommend highly with Tortoise upgrade. The warrior does not usually weaken the city. The archers do that for them. Then a warrior comes in and delivers the final blow, but to do this they must first survive the enemy archers or wall onslaught. I also recommend this on single player as well. The CPU opponent always gets walls. A warrior waits until the archers or siege units to weaken the city then deliver the final blow.
After Tortoise promotion I go with the route that bests deals with the enemy I am attacking or threatened by.
Swordsman
Main Roles
1) They can directly attack cities (so long as the defense is not too high).
2) They can attack group of archers (with little to no archer support). If a swordsman has Totoise upgrade, they are a huge danger to all archers. This is a huge turn around in the game because archers are the supreme attack unit until now. Now archers are the support unit.
Promotion Suggestions (see warrior section)
Heavy Chariot
Just avoid making these. They are not worth it. The only time I have made these was when I had no iron or horse strategic resources. Even then I cringed while making them.
Horseman
They are the most versatile and powerful unit of the ancient era.
Main Roles
1) Attack Cities and units (except pikemen)
2) Out flank melee and range units with there Superior 4 movement points.
Strategies
1) Use them to roll over your opponents weak beginning defenses
2) Destroy weakened units
3) Pilliage and attack. It costs 3 movement points to pilliage and you can still attack in same turn with enough movement points. With promotion you can pilliage for with 1 movement point. This can allow your unit to completely demolish a district in 1 turn.
4) Attack your enemies. Draw in the enemy fire. Then retreat and heal. This is one of my favorite tactics and it works so well because of their superior movement and high attack and defense. Let them take the heat so that your weaker support units (like archers) will not die.
Spearman
I usually avoid making these early on unless my opponent has horsemen and I do not. Be aware that their greatest weaknesses are that they are not early upgradable and archers. I like to think of spearman as weak on start, but strong on finish (due to it's promotions). If a spearman gets the right promotions they will be a force in a game. The problem is that online games moves very quickly throughout the ages, so a spearman will not usually get their time to shine online. Also they will need to survive long enough to get the promotions. Since archers are the main offensive unit early on they will be very vulnerable. In my opinion though, in standard speed games they are a better unit to get.
Main Roles
1) They can kill cavalry units
2) They help deal final blow to city
3) They can defend you cities better against calvary units.
4) Support Bonus. The Square promotion is awesome. If you get a group of 3 or more spearmen together with this promotion they will be tough in early game. A normal support bonus provides +2 strength to adjacent unit. with square promotion an adjacent unit get +4. Get 4 spearmen together they can boost each other by +12 strength.
Strategies
1) Like warriors avoid group of archers. Archers or range units are always their kryptonite. Since they do not have a promotion to defend better against archers they are more vulnerable to attack this way.
2) Like warriors they too can deal final blow to cities
3) When promoted they adapt to the situation better then most other unit in the game. All their promotions are awesome.
Promotion Suggestions
I like all the promotions for a spearman. If you are up against calvary then stick to the left side. If against melee units stick to right side.
That is all for now. It is getting late. I will try to add more to this tomorrow. I still have more to say on all the units I have listed. And I need to add more units too like catapult and Battering Ram. I know people will have their differences with me on some of things I have said. If you are one of those people then construct a good argument why I am wrong. List the reasons clearly so we could have a good debate. And perhaps you may change my mind...