Help Apache's mod_rewrite, please...

Hello,

I need http://mysite.com/?123 to show url.php?id=$1
I've came up with

RewriteEngine On
RewriteBase /
RewriteRule ^?([0-9]+)/?$ url.php?id=$1 [L]

Code (markup):

but that does nothing, but give me a "500 Internal Server Error".

Can someone please help.

Thanks