<?php
$recentposts = get_posts('nopaging=1');
$thumbs = array();
if( count( $recentposts ) ) {
  foreach( $recentposts as $p ) {
    $thumbs[] = '<a href="' . get_permalink( $p->ID ) . '">' . get_the_post_thumbnail( $p->ID ) . '</a>';
  }
}
echo '<ul class="gallery">';
foreach( $thumbs as $thumb ) {
	echo '<li><span>';
  echo $thumb;
	echo '</span></li>';
}
echo '</ul>';
?>