Researchers uncover cave pearls containing ancient artifacts in Ain Joweizeh spring tunnel

Researchers from the Hebrew University of Jerusalem uncovered rare cave pearls containing man-made objects within an ancient subterranean water system near Jerusalem. Their findings were recently published in the scientific journal Archaeometry.

Cave pearls are a rare type of speleothem, or mineral deposit, that resemble pearls. They form due to the slow crystallization of calcium carbonate on sand grains or other small particles, typically ranging from fractions of a millimeter to 30 centimeters in diameter. The formation of cave pearls requires specific conditions: the presence of mineral-rich water, nuclei, a flat cave floor with a shallow pool of water, water movement in the form of drips or slow-flowing water, and changes in soil chemistry over time, as detailed by HeritageDaily.

The discovery was made during a study of the Ain Joweizeh spring system, also known as the Joweizeh spring tunnel, one of the oldest artificial water structures in the region. The spring tunnel was constructed in the central part of the Naḥal Refa'im Valley and spans 232 meters, making it one of the longest in the southern Levant. It was originally created during the Iron II B-C period, which spans from 900 BCE to 586 BCE, likely as part of a royal estate near Jerusalem, as reported by HeritageDaily.

Researchers discovered about 50 cave pearls in a previously sealed-off section of the tunnel designed to extract underground water from the aquifer. These cave pearls are the first natural formations in history to contain man-made objects, including pottery shards and ancient plaster dating from the Babylonian period to Byzantine times, according to Gazeta.ru.

The cave pearls were discovered in the second section of the Joweizeh spring tunnel, which is carved directly into the bedrock. The first section is built of hewn stone and roofed with stone slabs. The tunnel flows northwest into a wadi before contributing to the Refa'im stream southwest of Jerusalem's old city, as described by Phys.org.

Out of the 50 cave pearls, 14 contained fragments of ceramics, and two contained ancient plaster. Most of the ceramic fragments date to the Hellenistic (333–63 BCE), Roman (63 BCE–324 CE), and Byzantine (330–636 CE) periods. Some fragments date to earlier epochs, such as the Middle Bronze Age II (ca. 17th century BCE), and others potentially date from the Early Hellenistic, Iron Age, Persian, or Babylonian periods, according to Phys.org.

Particularly noteworthy are pieces of ceramics with a cobalt-rich glaze. These cobalt-rich ceramics were produced in Cyprus and Ephesus during the Hellenistic period. The imported lamp could have belonged to an engineer overseeing the construction project, suggested by Dr. Azriel Yechezkel.

"Our initial research focused on mapping and surveying for archaeological artifacts within the spring tunnel. Cave pearls, a rare type of speleothem, were not the primary objective of our investigation. The discovery of these formations, and even more surprisingly, the presence of archaeological remains like pottery shards within them, was an unexpected and significant find," Dr. Yechezkel noted.

The formation of the cave pearls is presumed to have begun during the Hellenistic period. The flow of water in the Ain Joweizeh spring provided rotation to the nucleus of the cave pearls, causing them to become evenly coated and forming a spherical shape similar to a pearl formed in a mollusc. Unlike most speleothems, which take thousands of years to form, cave pearls can form over a few hundred years. This phenomenon is described as the "first of its kind" by HeritageDaily.

The discovery also reveals changes in the Ain Joweizeh spring's discharge and environment over the centuries. Evidence suggests that the Joweizeh spring tunnel was repeatedly reconstructed and used throughout the Roman and Byzantine periods before it was abandoned. Besides ancient looting, the only evidence of more recent visitation is the installation of a clay pipe through the tunnel, which was laid down in the 20th century, as reported by Phys.org.

The findings of ceramics and plaster confirm the active use of the tunnel during the Hellenistic period, with evidence of significant renovations. Spring tunnels are artificial tunnels designed to extract subsurface water from a perched aquifer and bring it to the surface.

This article was written in collaboration with generative AI company Alchemiq