One of the strangest, most enlightening things to do in Jerusalem is to visit the Wall Tunnels, a subterranean network along the western base of the 2,000-year-old Temple Mount.

The excavation lies at the heart of a dispute over whether Jews or Muslims have sovereignty over the holy site -- and whose archaeologists might have caused potentially catastrophic weaknesses that have appeared in the massive retaining walls.

Unlike the open, expansive walls on the southern and eastern sides of the plateau built by Herod the Great, the west wall is mostly hidden beneath the labyrinth of streets, homes and shops in the Old City of Jerusalem.

In Herod's time, around the birth of Jesus, the entire boxlike platform would have appeared on the horizon in stark, sunlit whiteness. On top, like the top layers of a wedding cake, would have been the Second Temple, a grand structure on the site where Jews believe Solomon's Temple -- the First Temple -- had stood 900 years earlier.

In A.D. 70, Roman soldiers destroyed Jerusalem, burning the Second Temple and pushing the rubble over the walls. The street elevation near the 37-acre Temple Mount rose in subsequent centuries, as various rulers built over the debris of previous cultures, often with massive arches to support new streets and neighborhoods.

This is what you see when you walk the tunnels, 20 to 30 feet below the surface: arched caverns made of rough-hewn stone blocks; ancient cisterns and water systems; paved avenues that two millenniums ago opened to the sky.

It's very dark in the tunnels, except for occasional spotlights, and eerie. If you're claustrophobic, don't go. At one point the main tunnel, the length of five football fields, narrows to three feet. The tour guide points to evidence of Herod-era workmanship and extraordinary feats of Roman engineering, including placement of an 11-by-40-foot foundation stone that weighs more than 600 tons.

There's an aura of secrecy that is not imagined.

After the 1967 Six-Day War, when Israel regained control of the Old City and the Temple Mount, Israeli archaeologists began digging out the base not far from the exposed western portion known as the Wailing Wall. For 15 years, they worked in secret, removing dirt bucket by bucket out of view of the Muslim authorities the Israeli government allowed to retain guardianship of the site.

Like Jews and Christians, Muslims trace their lineage to Abraham. They believe that here, on the mount they call Haram Sharif, the Noble Sanctuary, Abraham bound and almost sacrificed Ishmael. (Jews say it was Isaac who was bound here.) They built the 7th-century Dome of the Rock to mark that spot and the location from which the Prophet Muhammad rode a horse on his Night Journey to Heaven.

Angered by Muslim claims to exclusive rights to the site, Jewish archaeologists sought evidence linking the buried wall to the early temples and to get close to the "Holy of Holies," a chamber they believe lies about 100 feet from one of the tunnel rooms.

Officials of the Waqf, the Islamic trust overseeing the mount, learned of the archaeological dig and argued that excavations could compromise the wall's stability.

The situation exploded when an Israeli archaeologist broke through the wall into a chamber beneath the Dome of the Rock, where he encountered a Muslim official. A fistfight broke out, then an all-out political battle. Israeli authorities agreed to stop the work for a while, plug up the hole and stay on the outside part of the wall.

Tempers calmed and work resumed. But in 1996, Israeli archaeologists did what even many Jews thought ill-advised. In the darkness before dawn, they broke the surface at the end of the tunnel, creating an exit into the Muslim Quarter of the Old City.

The breach set off three days of protests in Jerusalem and Gaza, resulting in 66 deaths -- 52 Palestinians and 14 Israelis. At one point, Israeli police stormed the Temple Mount, killing three men who were throwing rocks on Jews praying at the Wailing Wall below. Violence continued for more than a year.

The current intifada, or Palestinian uprising, also originated on the mount. Two years ago, the visit of now-Prime Minister Ariel Sharon incited a riot.

Since then, non-Muslims have not been allowed to visit the Noble Sanctuary -- a restriction that allowed the Waqf to proceed with its own unapproved excavations: digging out an area known as Solomon's Stables at the southeastern corner of the mount to create the country's largest mosque.

Israeli officials believe this work has weakened an adjacent wall to the point of imminent collapse. A minor bulge examined two years ago on the south wall has widened to more than 100 feet and protrudes more than three feet, and the weight of 400,000 Muslims expected to visit the mount on Nov. 6, the beginning of Ramadan, could bring the wall down, they warned.

Muslim authorities accused the Jews of creating the problem with extensive excavations outside the wall and refused to allow Israeli scientists to examine the wall from the inside.

Meanwhile, a new bulge developed on the west wall to the right of the Wailing Wall. Dark moisture stains suggest that water seeping from a garden above is creating pressure on the wall, according to the Israeli Antiquities Authority.

After much bickering, the two sides agreed to allow the Jordanian government to mediate the south wall bulge, the one of greatest concern. Two weeks ago, Jordanian workers began making repairs.

Whatever the reasons, the edifice a wall tunnel guide called "the largest and most complicated building project in the world" has shown frightening signs of instability.

In a religio-political atmosphere where a tunnel exit and a government official's visit precipitate months of bloodshed, what might a wall collapse with thousands of casualties bring?

In 1996, the opening of a tunnel exit, in background at center, in the Muslim Quarter of the Old City ignited months of violence.A young man prepares for Monday morning prayers at the exposed section of the wall known as the Western Wall, or Wailing Wall.Israeli officials say a large bulge on the south wall could endanger Ramadan crowds next month. Israeli excavations along the base of the hidden part of the west wall revealed arched supports added in Roman or medieval times to support the raised street level.Looking east toward the Temple Mount, which Muslims call the Noble Sanctuary, across the Old City of Jerusalem. Most of the west wall is buried under layers of civilization.