<?php
//wp_nav_menu_select(array(
  //'theme_location' => 'main_navigation', // your theme location here
  //'walker'         => new Walker_Nav_Menu_Dropdown(),
  ///'items_wrap'     => '<select>%3$s</select>',
//));
?>

<nav class="main-nav nav-select-menu">
<div class="container">
<?php wp_nav_menu( array( 
'container_class' => 'main-menu', 
'theme_location' => 'main_navigation',
'fallback_cb' => 'oriont_nav_fallback'
) ); 
?>
</div>
</nav>