Top level blog not working at all

I have wordpress mu setup with 1 top level blog and a couple subdomain blogs that has been working fine for some time. Today I added the following code to my theme folder’s functions.php file (don’t ask), after which I have been unable to access the top level blog in any way (admin, posts, homepage, etc):

function get_the_taxonomy( $id = false ) {
	global $post;

	$id = (int) $id;
	if ( !$id )
		$id = (int) $post->ID;

	$categories = get_object_term_cache( $id, $taxonomy );
	if ( false === $categories ) {
		$categories = wp_get_object_terms( $id, $taxonomy );
		wp_cache_add($id, $categories, $taxonomy.'_relationships');
	}

	if ( !empty( $categories ) )
		usort( $categories, '_usort_terms_by_name' );
	else
		$categories = array();

	foreach ( (array) array_keys( $categories ) as $key ) {
		_make_cat_compat( $categories[$key] );
	}

	return $categories;
}

You can see what I’m talking about at https://climbingnarc.com.

I’ve tried removing the code from the functions.php file and a few other things but nothing has made a difference.

What’s strange is that I can still access the subdomain blogs and their admin interfaces, just not the top level blog.

What did I do???