Wire and nails and make sure you hit studs.
Timothy: Maybe this will help:
You will want to put an anchor in the wall and then screw into that anchor!
Hello Timothy, if its really heavy-I would suggest the rail over the edge cleat locking system.
Here's a link to consider with very heavy art or heavy weight mirror. I hope this helps!
They sell library hangers at Lowe's. It's a steel bar that you attach to the wall with screws. It works great!