Importance of unit depth/width?

Hi, I'm new here but I assume this is the correct section of the forums to post in.

One of the things that has always puzzled me since I started playing Total War games is how unit width affects how they perform. I've never really been able to find out much information in game from the tutors, or in the manual.

So I wondering if anyone could highlight the benefits/disadvantages of having units 2 ranks deep or having one very deep and thin.

I always thought that having archers two ranks deep would be the best option, as this ensures that the most amount possible have a direct line of sight to the target. However I read a thread recently about how apparently the other men in a missile unit are transparent to each individual in the unit, and therefore having them in a square block is no less effective than a long wide line of them. On the contrary, the same thread went on to say that they reported a greater accuracy from the unit with a more narrow/deep formation, as the fire was more concentrated, especially when shooting on castles during sieges.

To test this I had longbowmen kill a unit of highland rabble and timed how long it took them to kill/rout the unit. With wide and narrow formations the time to kill/rout wasn't effected at all. Then for a further test I tried this in a large army fight to see if there was any significant difference, this is what surprised me. When I had the archers in the traditional wide formation, the enemy were often caught in a cross fire as they moved forwards, as the arrows would be coming from a wider angle of directions. This would seem like ideal, it means that every unit on the front line sustains some casualties, but no unit sustains enough to cause them to waver in morale. With the compact deeper formations, it meant that virtually all the shots were coming from a very concentrated angle. The result was that the one unit I had all my archers target was crippled completely and began to waver in morale. More importantly this left a massive weak spot in the enemy armys front line. I immediately sent a heavy cav unit (also in box formation I might add), the unit began to rout before my cavalry charge reached it, and meant the cavalry had a head on charge into the enemies second line which happened to be archers who also routed instantly. Two units routed without me taking barely any casualties, and breaking their lines to collapse their army from within with my cavalry. I know this is only against the computer, but the comparison in results still matters a lot in my opinion.

Then there is the case of infantry, I again assumed that a wide as possible unit would be best, to ensure the most amount of people get into combat as possible, however since I started experimenting with deeper ranks, I am having much more success. For example spear militia are more likely to resist a charge, Armoured swordsmen are more effective when attacking, as they are less likely to have individuals become surrounded. More interestingly still was the effect it had on Cavalry charges. I found that the unit was much more likely to stay in a formed charge when in a more square formation than wide, and that although less of the enemy unit are struck by the initial hit of the charge the ones that were hit were effected more than usual, and the cavs drove much deeper into the opposing unit. This meant that the enemy unit seemed more likely to rout because of the sheer devastation that occurred to the few that were hit. It also meant that although the cavalry become engulfed by the enemy unit as a whole instead of as individuals which usually happens then a wide formation is used, and this meant that when withdrawing for a second charge less of the horses were exposed and consequently less killed. Then there is the added advantage that a square unit can charge effectively in all directions instead of having to line up.

Anyone have anything to say on this? Really interested to see what people have to say.

For archers - I set my missiles in narrow columns when I know I will punch one hole in the enemy walls and I'll have to shoot trough it to get to the units behind. It's by far the most effective in such a case. When leading a field battle, I keep my archers in 3 or 4 lines deep formations depending on how many I have and how much infantry I have covering them.

The reason being, as you already noticed, that the momentum of a charge cuts trough thin lines like a knife trough butter, and broken lines means faster routing (or instant routing). In M2TW the units have "mass" as a hidden stat, and that affects their performance in relation to the opposing units/lines.

Of course a uint of spears in schilthorn will resists a charge better than a unit two lines deep, it makes sense if you think about it. As such I keep my lines relatively thick, but I only go for squares of infantry for city fighting. If you have superior units however, a thin line will envelop the enemy and start hacking from their less armoured sides than frontally. For example, fully upgraded armoured swordsmen versus run of the mill infantry - due to greater defence, you will lose almost no men, while the enemy line will crumble from the sides.