Harkadio Cave is located in the area of Mesaria of Tilos. More than 15.000 mammoth dwarf bones, dating back to 7.000 BC, have been found in the cave. Also the palaeontological excavation that took place in 1971 in the cave brought to light deer bones, which lived 140.000 years ago.
These small mammoths have adapted to the environment since Tilos was cut off from Asia Minor (12000-8000 BC). Slowly, however, this species began to disappear, probably due to the volcanic eruptions of Santorini and Nisyros, as the bones were buried under a thick layer of volcanic ash.
Neolithic ceramics, clay tools and clay shells of all periods were also found in the Cave, proving the continuous habitation of the area as well as the Knighthood.