It continued the phalanx formation or shield wall of infantry armed with polearms in use during antiquity and the Middle Ages.
[1] The line formation was very successfully first used with combined arms in the Thirty Years War by the Swedish king Gustavus Adolphus the Great, at the Battle of Breitenfeld.
Movement in line formation was very slow, and unless the battalion was superbly trained, a breakdown in cohesion was virtually assured, especially in any kind of uneven or wooded terrain.
In addition, the line formation was extremely vulnerable to cavalry charges, from the flanks and rear, and these attacks usually resulted in the complete breakdown of cohesion and even destruction of the unit unless it was able to "form square".
The famous "Thin Red Line" of the 93rd (Highland) Regiment at the Battle of Balaklava successfully held against a Russian cavalry attack, a rare occurrence.