apache重定向页面的规约

apache重定向页面的规则
就是伪静态页面 我想访问根目录下的cs.html就等于访问cs.php 
然后我在.htaccess里这样写了

RewriteEngine on
RewriteRule cs.html$cs.php [L]

可是提示
---------------------------------------------------------
Not Found
The requested URL /cs.html was not found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

-------------------------------------------------------------

到底要怎么样写？ 求解

[解决办法]
试试：

PHP code

RewriteRule ^cs.html$ cs.php [L]