If you want to redirect all pages on a site to an error page, you'd think you could use a Redirect with something like 'if not pageX send to pageX' but I cannot find an example of that actually working. Instead, you must use Rewrite

LoadModule rewrite_module modules/

RewriteEngine On
RewriteCond %{REQUEST_URI} !=/splash.html
RewriteRule ^ /splash.html [R=301]