Altar of Mithras. Mithras was god of a mystery religion in the Roman Empire from about the 1st to the 4th century.
<a href="//commons.wikimedia.org/wiki/User:HOWI" title="User:HOWI">HOWI</a> - <sup> Horsch, Willy </sup>
CC BY-SA 4.0
<span class="int-own-work">Self-photographed</span>