Historical map of borders between Bulgaria and Ottoman Empire in <a href="https://en.wikipedia.org/wiki/Eastern_Thrace" class="extiw" title="en:Eastern Thrace">Eastern Thrace</a> between 1912 and 1919. In Bulgarian
<a href="//commons.wikimedia.org/wiki/User:Ikonact" title="User:Ikonact">Ikonact</a>
CC BY-SA 3.0
<p><span class="int-own-work" lang="en">Own work</span>
</p><p>Data:
</p>
<ul><li>SRTM3</li>
<li>OpenStreetmap</li></ul>