Originally Posted by
Sheogorath
On the subject of formations...
...
The square is a typical defensive formation, best used to ward off cavalry. Often I hear it quoted that 'a square has only been broken by cavalry twice' or some other such nonsense. This is, of course, quite silly, but some have imbued the square with legendary cavalry-stopping abilities. While no doubt advantageous to the infantry in that it is impossible to flank a complete square, it is also essentially composed of four lines of infantry. Thus, if a charge takes place, it cannot be to the rear or flanks, which would probably lead to some casualties amoung the horses, but, in the end, a determined cavalry (with sufficient numbers) should be quite capable of destroying a square.
As mentioned, a square's advantage lies in its lack of flanks. All charges and attacks must be made to the 'front' of the formation.
However, a square is both totally immobile, and vulnerable to artillery, since artillery fire will pass through at least two lines of soldiers no matter the direction. Musket fire also presents an issue, since a square is typically even tighter than a line, and moving your men closer together makes them easier to hit.