Antique Roman <a href="https://en.wikipedia.org/wiki/Flat_glass" class="extiw" title="en:Flat glass">window glass</a>. Found in a Roman castle in Straubing, Bavaria, Germany. Dated to approx. 1st to 4th century A.D. Photographed at Gäubodenmuseum, Straubing, Germany.
<a href="//commons.wikimedia.org/wiki/User:Bullenw%C3%A4chter" title="User:Bullenwächter">Bullenwächter</a>
CC BY 3.0
<span class="int-own-work" lang="en">Own work</span>