Resource id #3?

I guess I'm not getting this, but I'm trying to run an
aggregate function (MAX) on a simple table with PHP. I want
to find the largest id (an integer) and nothing else. It
doesn't matter what is in that row, I just want the largest.
I thought I had it with this:

$maxid = query("SELECT MAX(id) FROM mytable");

// query () is a function that queries the DB with the sql

But when I echo "$maxid"; I get "Resource id #3". That is
not what I wanted. I was hoping I would get "25" or "30" or
whatever the highest number in the 'id' column is. What am I
missing here?

/mark