Custom page posts

Hello, i have made a custom page template with posts, i have in my page about 20 posts, but in the page only appears about 6.Ho you have any idea?Thanks in advance, here is the page template code:

<?php
/**
* Template Name: Archive
*/
/*Use Bootstramp*/
get_header(); ?>
<div class="container">
<div class="row">

<div id="PostData">
<?php
global $post;

$theposts = get_posts();

foreach ( $theposts as $post ) :
  setup_postdata( $post );
echo '<div class="ArchiveThumb">';
  echo get_the_post_thumbnail($post_id,'medium');
echo '</div>';
  ?>

	<p class="PostName"><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></p>

<?php endforeach;
wp_reset_postdata(); ?>

</div>
</div>
</div>

			<?php

			?>

		</main><!-- #main -->
	</div><!-- #primary -->

<?php

get_footer();