The Great Theater of Ephesus 
At an estimated 25,000 seating capacity, it is believed to be the largest outdoor theater in the ancient world.
<a href="//commons.wikimedia.org/wiki/User:AdMeskens" class="mw-redirect" title="User:AdMeskens">Ad Meskens</a>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>