Why is a drum round not square?

Hey, I was asked to research this for an assignment in my Maths Class. I googled it, and advanced googled it however I only found 1 site which gave a whole array of answers and weren't all that mathematical. I was wondering if anyone could give me a mathematical answer? (That is easy to understand but not too easy (if that makes any sense).

**Why is a drum round and not square?**

The only thing I can think of is something to do with the resonance of the sound and being lost in the corners of the drum and the round shape creating a more even 'surface' for the sound to reverberate from. ???

If anybody could help me out I would very much appreciate it, thanks.