I am attempting to map/mask a subfolder to another folder on a single server. I have tried it lots of occasions before however i can't get this work correctly. I would like the consumer who accesses directory "a" to determine "oldsite/a" rather, however i don't want these to be rerouted, in order to begin to see the new address within the browser.

<IfModule mod_rewrite.c>
        RewriteEngine on
        Options +FollowSymlinks
        RewriteRule ^\.htaccess$ - [F]
        # Maintain support for old structure
        RewriteRule ^a/([0-9]+)$  oldsite/a/$1?redirected=1 [QSA,L]
</IfModule>

I have attempted various combinations with RewriteBase, etc. Rather than the consumer seeing "domain.com/a/1234" they're rerouted to "domain.com/oldsite/a/1234?rerouted=1".

Works out the statement didn't have a closing forward-slash prior to the query string.

RewriteRule ^a/([0-9]+)$  oldsite/a/$1/?redirected=1 [QSA,L]