When a floor begins to give way in one of the 2,000-year-old tunnels underneath the Old City during excavations, archeologists get excited. Holes in the floor can be dangerous, but they’re also a sign that there are even more layers of history underneath, waiting to be discovered.Recently, when part of the floor collapsed in a massive underground drainage ditch deep below the Western Wall as archeologists were taking it apart to see how the floor was constructed, they could barely contain themselves.They were so excited to see what was down there that they couldn’t wait for additional lighting, and used their cellphones to see what they had found. Chief archeologist Eli Shukron, who has been digging around Jerusalem for 25 years, was his first to stick his head in the hole. He was blown away by the size of the room they had uncovered.Based on previous research and excavations in the area, Shukron was immediately convinced they had stumbled on an enormous underground well from the First Temple Period. The finding is significant because it is the first evidence of stored water next to the Temple. Previously, experts believed that pilgrims and residents used to hike to the Gihon Spring – located in a wadi at the bottom of the City of David park – in order to get water for rituals and daily life around the First Temple.“It gives us an opportunity to understand their day-to-day life,” said Shukron on Thursday.At roughly one-tenth the size of an Olympic swimming pool, the reservoir measures 12 meters by 5 meters by 4.5 meters and can hold approximately 250 cubic meters of water.Shukron dates the reservoir to the First Temple Period because it uses the same type of plaster as other reservoirs in the Gihon Spring area, from the same era.He is fairly certain that the pool was a public reservoir because the private wells could only hold a few dozen cubic meters of water.While the reservoir was in use, spring water running downhill from the Temple Mount would have seeped through one side of the reservoir and filled the entire room to capacity. On Thursday, a pool of fresh water was still standing at the bottom in one of the corners, even though it is the end of summer.Dr. Tvika Tsuk, the chief archeologist of the Israel Nature and Parks Authority and an expert on ancient water systems, said the reservoir was similar to ones found in Beit Shemesh and Beersheba from the same time period.“Presumably the large water reservoir, which is situated near the Temple Mount, was used for the everyday activities of the Temple Mount itself and also by the pilgrims who went up to the Temple and required water for bathing and drinking,” he said. The excavations were carried out by the Antiquities Authority, funded by the Ir David Foundation, and with the support of the Nature and Parks Authority.Even today, the handprints of the laborers who added the plaster are still visible.The reservoir’s discovery was presented on Thursday at the 13th annual City of David Studies of Ancient Jerusalem conference, which deals with findings from the past year in the City of David archeological park.The drainage channels underneath the Western Wall Plaza are part of a giant engineering project undertaken in the Second Temple Period. Even the debris filling the water channels contains unique discoveries: shards of pottery dating back 2,000 years, an ornamental golden bell that possibly belonged to a high priest, and seals – one of which offered the earliest written reference to Bethlehem.