I remember getting into an argument with one of my professors in a music history course my junior year because he insisted that Ionisation was the first piece of music written for percussion alone.  No, I replied, Ionisation was completed in 1931, but Amadeo Roldan's Ritmica no. 5 and Ritmica no. 6, both of which are scored for nothing but traditional Afro-Cuban percussion instruments, were composed the year before.  "Check your facts again," he told me.  I think that was his implicit way of saying, "Keep your mouth shut.  You percussionists are getting the good end of this little historical inaccuracy."  Sometimes I wish I'd listened to him.

It is true that the Ritmicas predate Ionisation.  If you really want to get persnickety, Futurist composer Luigi Russolo's compositions for his intonarumori (written in the years shortly before World War I) predate them both, and are technically scored strictly for "percussion instruments," though none of his instruments survive to the present day. (By the way, Russolo is definitely worth checking out.  His inventions are intriguing, and despite the fact that he lacked formal musical training, his views on the evolution of music in the twentieth century are quite remarkable.  Look up his manifesto The Art of Noises for more information.)

So, with at least Russolo and Roldan (and likely a few more composers we don't know about) beating Varese to the punch, why does Ionisation get all of the glory?  Because, to the best of our knowledge, it's the first GOOD piece of music written solely for percussion.   By all accounts, Russolo's noise music compositions were little more than a novelty--Varese himself said as much, if page 307 of Morgan's Twentieth-Century Music is any indication.  The Ritmicas, while written by a composer with formal training, do little besides showcase the sounds of traditional Afro-Cuban instruments and demonstrate basic characteristics of Cuban folkloric style (no. 5 is marked "son" and no. 6 "rumba").  It is only with Ionisation that we begin to see music written for percussion that takes advantage of the same sophisticated compositional techniques that other instrumentalists had been experiencing for decades.  Ionisation wasn't the first piece written for percussion, but it was the first piece of the modern (lower-case "m") percussion era.  It nearly singlehandedly took music for percussion from novelty to legitimacy.  Who knows, if not for Varese percussionists might still be required to learn how to pull bananas out of resonator tubes and tapdance while playing xylophone.  So these days, when I hear someone mention that Ionisation was the first work written solely for percussion, I don't correct them.  Call it academically irresponsible, but I don't lose sleep over it.

One more quick thing:  Did anyone happen to see the fall percussion ensemble concert?  One of the pieces on the concert, Carl Schimmel's Serving Size 4 Bunnies, also makes use of something seen largely as a novelty (humor, in this case) in the context of a very seriously-composed piece of music.  Squeaky pet toys, popping balloons, a contrapuntal kazoo duet, and shouts of "If I had a leg I would kick in your head I would kick in your head I would kick it" are juxtaposed with all-interval tetrachords, complex tone-row manipulation, and an entire movement based on the Fibonacci sequence.  If anyone would like to listen to a recording or see a score, let me know.