The massive ancient reservoirs that remain viewable today in Jerusalem’s Old City had serviced Jews making pilgrimages to the Second Temple some 2,000 years ago, according to a soon-to-be-published research paper.

Jerusalem contains a large number of these ancient pools. A massive cistern named the Pool of Israel—more than 360 feet long, 111 feet wide and 78 feet deep—is situated next to the Temple Mount. The Pool of Hezekiah lies among the houses of the Christian Quarter. Jerusalem residents are also familiar with the Sultan’s Pool, which was converted into an open-air venue for public performances; two pools located on the Church of St. Anne’s property; a deep pool seen on Western Wall tours; and the Shiloah (Siloam) Pool, which was discovered under the City of David.

“While residents of Jerusalem had private wells under their homes and the ruling authorities had aqueducts, another solution was needed for the masses of pilgrims. The visitors used water for drinking, cooking and other day-to-day tasks. Two of the pools were also used for ritual cleansing,” Dr. David Gurevich, an archaeologist at the Hebrew University of Jerusalem who specializes in the holy city’s history during the Second Temple period, told Israel Hayom.

“These large complexes are the elephant in the room that researchers have ignored. Even though some of the pools were excavated and researchers suggested the use of individual pools, they ignored the larger picture. The question was never asked, ‘What are these facilities doing specifically here?’ It turns out there has never been another city on the Mediterranean coast with such a large amount of these pools of water,” said Gurevich.

The University of Haifa and Harvard University launched the study, which is due to be published soon in Palestine Exploration Quarterly, a prestigious European-printed archaeology journal.