Experts say they’re baffled by a one-of-a-kind series of channels carved into the bottom of a cliff in Jerusalem almost 3,000 years ago.

They say the trenches, cut into the bedrock, appear to be designed for soaking large quantities of something, but they don’t know what.

Their best guess is either flax to make linen, or dates for silan.

But researchers from the Israel Antiquities Authority (IAA) and Tel Aviv University admit they can only speculate.

The location of the channels, in the City of David National Park just outside the Old City of Jerusalem, strongly suggests a connection with either the First Temple or a royal palace.

Yiftah Shalev, senior researcher at IAA, said: “We realized that we had stumbled on something unique, but since we had never seen a structure like this in Israel, we didn’t know how to interpret it. Even its date was unclear.”

They brought in experts, including a police forensic unit, to check for pollen, organic remains or traces of blood that would provide a clue, with no success.

The excavations, carried out at the Givati Parking Lot, have so far uncovered two distinct structures, believed to be part of a single installation.

The first, at the northeastern end, includes a series of at least nine channels at ground level, together with seven drainage pipes from the cliff top. The second structure, 20 meters to the south, is very similar but has five channels.

“Despite some differences in the way the channels were hewn and designed, it is evident that the second installation is very similar to the first,” said Prof. Yuval Gadot of Tel Aviv University’s Archeology and Ancient Near Eastern Civilizations Department.

He said the discovery of a second structure had yielded information that allowed them to date the last time it was used — the end of the ninth century BCE, during the reigns of King Joash and King Amaziah – but did not resolve the mystery of its purpose.

“The central location of the channels near the city’s most prominent areas indicates that the product made using them was connected to the economy of the Temple or palace,” Gadot added.

“Ritual activity includes bringing agricultural animal and plant produce to the Temple. Many times, Temple visitors would bring back products that carried the sanctity of the place.”

The fact that the channels flow in different directions, and the absence of a drainage basin, suggests their function was to soak products and circulate liquid, rather than drain it, said Shalev.

“The production of linen, for example, requires soaking the flax for a long time to soften it. Another possibility is that the channels held dates that were left out to be heated by the sun to produce silan [date honey], like similarly shaped installations discovered in distant places such as Oman, Bahrain and Iran.”

Experts believe what they have uncovered so far is part of a much larger, industrial-scale installation.

The next step is to take further soil samples in the hope that analysis will shed some light on the mystery.

The excavations are being funded by the Elad Foundation, which manages the City of David National Park. The public will be able to see them next week during the 24th City of David Studies of Ancient Jerusalem conference.