Deep grooves cut into the bedrock date to the biblical Kingdom of Judah, and bolster the theory of Jerusalem’s early expansion. But what purpose they served remains a riddle.

Archaeologists excavating in Jerusalem have uncovered a network of mysterious channels dating back to the days of King Joash and Amaziah, some 2,800 years old.

The installations are the first of their kind ever discovered in Israel, the IAA said in an announcement Wednesday. The national park in which the structures were found contains the City of David archaeological site—considered by most scholars to be the location of the original settlement at Jerusalem.

The grooves, cut into the bedrock, were likely used to soak some kind of product, though it is unclear what exactly the ancient Jerusalemites were making there, the Israel Antiquities Authority and Tel Aviv University said in a statement Wednesday 30th of August 2023.