The marching aspect of marching band started as a direct effect of the military band's influence on the marching band, but more importantly, marching serves a few purposes - it keeps the musicians in tempo by making them actively move in time, and it keeps the unit as a whole organized, not just a bunch of people walking around in sorta the same area.
There are also technical aspects of marching - the mechanics of the leg follow through and the foot placement/angle support the upper half of the body, especially for a wind player. If players didn't march, there would be a "wawawawa" in the sound for every time they clomped their feet on the ground.
Marching
just that a marching baritone
there's no such thing, but there is such thing as a brass marching band
a marching tuba would be called a sousaphone.
Cavalier Marching Band was created in 2003.
Marching
The troops begin marching to the battlefield.The marching band was spectacular.We are marching you down to the police station.
marching in two lines
Marching Out was created in 1985.
Marching In was created in 1970.
Marching quints have one more small drum, called the sprock, than the marching quads do.
The troops begin marching to the battlefield.The marching band was spectacular.We are marching you down to the police station.
just that a marching baritone
Marching Illini was created in 1907.
The Marching Morons was created in 1951.
Ants Marching was created in 1995.
Marching Knights was created in 1979.