Marching band styles

Marching bands are categorized based on primary function, instrumentation, and style - although many organizations may fill multiple roles.
Military bands and Corps of Drums were historically the first marching bands. Instrumentation varies, but generally contains brass, woodwinds, and percussion. Given their original purpose, military marching bands typically march in a forward direction with (no variation of) straight lines. Music is performed at a constant tempo (120-140) to facilitate the steady marching of the entire military group with which the band is playing.
http://en.wikipedia.org/wiki/Marching_band