A keystone, in a tower of the "Alcazar de los Reyes Cristianos" (<i>Fortress of the catholic kings</i>), in Cordoba, Spain.
<a href="//commons.wikimedia.org/wiki/User:Jebulon" title="User:Jebulon">Jebulon</a>
<span class="int-own-work" lang="en">Own work</span>