While Napoleon is best known as a master strategist and charismatic presence on the battlefield, he was also a tactical innovator. He combined classic formations and tactics that had been used for thousands of years with more recent ones, such as Frederick the Great's "Oblique Order" (best illustrated at the Battle of Leuthen) and the "mob tactics" of the early "Levée en masse" armies of the Revolution. Napoleonic tactics and formations were highly fluid and flexible. In contrast, many of the "Grande Armée"'s opponents were still wedded to a rigid system of "Linear" (or Line) tactics and formations, in which masses of infantry would simply line up and exchange vollies of fire, in an attempt to either blow the enemy from the field or outflank them. Due to the vulnerabilities of the line formations to flanking attacks, it was considered the highest form of military manoeuvre to outflank one's adversary. Armies would often retreat or even surrender if this was accomplished. Consequently, commanders who adhered to this system would place a great emphasis on flank security, often at the expense of a strong centre or reserve. Napoleon would frequently take full advantage of this linear mentality by feigning flank attacks or offering the enemy his own flank as "bait" (best illustrated at the Battle of Austerlitz and also later at Lützen), then throw his main effort against their centre, split their lines, and roll up their flanks. He always kept a strong reserve as well, mainly in the form of his Imperial Guard, which could deliver a "knockout blow" if the battle was going well or turn the tide if it was not.