Newbue to Civ. Q about units in Revolution

I am new to Civ in general and love this game. My q is this. Is it possible to attack a city ( or any unit I guess) with more than 1 unit or army at a time? How do I take out a city/ unit that is superior to one of my units or armies? Also the game says ANCan stack as many units as u like when u have at least 3 that's an army. The problem is that if I try to stack another unit on an ecsisting army it doesn't work. Shouldn't I be able to stack 4,5,6... Units high??

Sorry about all the newb qs but the is the 1 st time I've play Civ in any form. Thanks everyone!

The Army (or Wing or Fleet) is the largest functional entity - you can't create uber-armies.

Here's some tricks to attacking cities:

Attack from a Hill whenever possible. Your units get a bonus
Never attack across a river (penalty for many units)

Make sure your armies are veterans. Infiltration and Blitz help too

You will (almost) never take a city with a single unit, unless you way outclass the defender (a tank against an archer army usually works

If you have multiple units, and one has a Great General, attack with other armies first (assuming the armies are roughly equivalent). You don't want you GG dying before he can boost your remaining units

Sometimes talking to other leaders will reveal information about a particular city - what's being built there, how many units, etc.

Naval support - this is a biggie. Park a fleet of ships next to the city you're attacking. The navy adds about 1/3 of its strength to the attack. If you can get your attacking units next to the ship too, it will help defend them when the enemy counterattacks.

Spies can remove the fortification bonus that defenders get in a city. They can also knock down walls (though you will typically destroy a random building).

Each army / unit attacks separately. So stacking 3 legions together gets you three attacks with strength 2 rather than one attack with strength 6. Thus, in most cases, you will want to make armies for the combined attack & defense. Armies are made from 3 of the same unit, no more no less.

Unlike some games (Civ 4?) there's no limit on the number of units / armies (of a single Civ) which may be occupy a single square (stack). If you attack a stack, you attack only a single army/unit in the stack (typically the one with the highest defensive value, but not always).

As for attacking a superior defensive force, here are some hints:
1. Attack with armies!
2. Place a galleon, cruiser, or battleship (or better yet, a fleet) adjacent to where you are attacking for naval support. Plus, galley & galleon crews will act as scouts.
3. Attack from hills when possible & never attack across a river or from a boat. Attack from forests to get the defensive bonus for the counter-attack.
4. Use Veteran units; - remember 1 veteran unit is all it takes to make a veteran army and an elite unit makes an elite army.
5. Use catapault / cannon / artillery - but always escort with a defense.
6. Don't attack with just one unit / army - use multiple attackers in the same turn to wear down a superior force.
7. Use spies to destroy fortifications. Use spy rings to defeat defending spies.
8. Attack with your strongest attacker first for the best odds.

Thanks guys! This game is amazing, I just wish I knew what the he'll I was doing. I guess thar comes with practice.