Rocks at Dun Carloway Broch
They were built with no mortar.
"Dun Carloway was probably built some time in the 1st century BC, and radiocarbon dating evidence from remains found in the broch show that it was last occupied around 1300 AD." -- according to en.wikipedia.org/wiki/Dun_Carloway
(other websites, however, speak of more recent residences)