The two flank companies are designed for tirailleurs.

This would give a column of four divisions, and consequently twelve files deep; and as only two of these files could employ their fire, there would be much too large a portion of non-combatants exposed to the enemy's artillery.

In practice, however, we employ the two-rank formation, which, if the flank companies be detached, would give a column of attack eight files in depth, which is not objectionable.

If however, the flank companies should be present in the battalion, the depth of the column would still be ten files.
In the French service, each battalion is composed of four divisions, formed in either two or three ranks.

The two-rank formation is the one habitually employed.