Call a static block using xml in Magento 2

Call from Xml File:

 <block class="Magento\Cms\Block\Block" name="Promo">  
   <arguments>  
     <argument name="block_id" xsi:type="string">promo</argument>  
   </arguments>  
 </block>  

Call from Phtml File:

 <?php echo $block->getLayout()->createBlock('Magento\Cms\Block\Block')->setBlockId('block_identifier')->toHtml();?>  

Call from cms page or block:

 {{block class="Magento\\Cms\\Block\\Block" block_id="block_identifier"}}