Obviously cellists and bassists can’t march with their instruments. I think marching bands might have evolved from military bands and violins and violas are not loud enough to carry over a battlefield, but that’s mainly speculation. It doesn’t really explain why woodwinds are part of marching bands because most them are also not very loud. Drums and brass are quite loud compared to other instruments.

Violins, outside temperature changes, rain and occasionally bumping into the musician in front of you don't go together. The traditional marching band instruments are more robust.

Also violins, being held under the chin, might not be easy to march with. Agree with volume and temp/rain issues. But not every thing in art has a logical reason either. Why don’t heavy metal bands have tubas? Because they just don’t fit stylistically.

And... youtu.be/EMm8Sm4v5PM

I'll note that some marches (often coronation or funeral marches) involve strings (and a full orchestra) but don't really involve musicians marching. Some examples include the Radetzky March and the Pomp and Circumstance Marches.

@YourUncleBob - wouldn't want to bump into the guy in front, with a trombone in my mouth...

@ToddWilcox Well, cellists can march with their instruments, albeit awkwardly. I played in a group at the Dickens' Fair with a cellist who not only walked but danced with her instrument, supported by a band around her neck. But yeah, awkward at best.

Woody Allen would like a word with you....

Marching bands may not have strings, but some scatter bands do.

@Dekkadeci Marching bands don't necessarily play marches. Marches are often intended for other people to march to, like the graduate procession to Pomp and Circumstance, or the Wedding March. Marching bands frequently play pop music, they also march around while playing.

@YourUncleBob - very much so, but pushing the slide out over the guy in front's shoulder (or worse) is likely to get the rest of the trombone pushed down your throat..!

In the last century, violent conflict between opposing marching bands was a common occurrence. Brass and woodwinds inflict more blunt force trauma with less damage to the instrument.

@Carl Witthoft, I suppose no one else saw Woody's true, fictional documentary.

@ToddWilcox flutes actually make sense in terms of both the volume to project and the military history. Flutes (especially fifes and other small transverse flutes) have always been military instruments, specifically because they do project so well over long distances. And in modern marching bands, flutes in the upper registers easily cut through the whole band, piccolos even more so. Consider the fact that, in the modern orchestra, there are usually 2 flutes and 20-30 violins. Not saying 2 flutes is the same volume as 30 violins, but the fact that it's even possible tells you something.

Because otherwise it would be an orchestra. The definition of 'band' is 'no strings'.

@user207421 - not true! I've played in many bands with strings, and I'm not just counting guitars and basses. And in fact, several big band leaders call the band their 'orchestra'.

Former marching band geek here (French horn) who played violin in elementary school. Above all the reasons mentioned so far (volume, fragility), it just wouldn't be practical. Bowed instruments in close formation would be a nightmare - you'd be at risk of putting a bandmate's eye out. Your balance would be weird, especially for tight turns (at least with violins and violas). Violin and viola require a lot of upper body movement vs. fingering a horn, which would get tiring fairly quickly. Instruments get heavy 2/3 of the way through a parade.