/root
  .htaccess
  /config
    databases.yml
  /web
    index.php
    /images
      test.jpg

Options +FollowSymLinks +ExecCGI

<IfModule mod_rewrite.c>
  RewriteEngine On
  
  # we skip all files in /web
  RewriteCond %{REQUEST_URI} ^/web/
  RewriteRule .* - [L]
  
  # we rewrite all other files with .something to /web
  RewriteCond %{REQUEST_URI} \..+$
  RewriteCond %{REQUEST_URI} !\.html$
  RewriteRule ^(.*)$ /web/$1 [L]
  
  # !!! UNTESTED !!! ##################################
  # we check if the .html version is in /web (caching)
  RewriteRule ^$ /web/index.html [QSA]
  RewriteRule ^([^.]+)$ /web/$1.html [QSA]
  #####################################################
  
  # no, so we redirect to our front web controller
  RewriteRule ^(.*)$ /web/index.php [QSA,L]
  
</IfModule>

# big crash from our front web controller
ErrorDocument 500 "<h2>Application error</h2>symfony application failed to start properly"

<?php

/* according to .htaccess */
$_SERVER['SCRIPT_NAME'] = '/index.php';

define('SF_ROOT_DIR',...