By hello
Kebar Dam is an exceptionally early masonry arch dam, generally dated to around 1300. Its small reservoir is no longer used and is mostly filled with silt, making it a rare example of a very old dam that still stands but has effectively lost its original function. (en.wikipedia.org) Unusual technique: early arch-dam design in masonry, often cited as one of the oldest surviving examples of that structural idea. (iranicaonline.org) Why it remains: chiefly for historical and engineering significance. (en.wikipedia.org) Further information: https://www.iranicaonline.org/articles/band-dam/