On my return from Jordan, I found that it was and still is widely reported that an underground tunnel has been opened in Jerusalem and, as expected, some outrageous Palestinian comments made about the supposed danger to the Temple Mount, such as these:
The tunnel leading from the City of David in Silwan to beneath the walls of Jerusalem’s Old City, excavated by the Israel Antiquities Authority and announced to media fanfare Sunday, is drawing fire from Palestinians who claim it will damage the Temple Mount.
Fatah Revolutionary Council member Dimitri Diliani accused the Jerusalem municipality of Judaizing East Jerusalem and said the digging constituted a “direct danger to al-Aqsa.”
The tunnel in question was first discovered by Charles Warren in the 1870’s, recorded by subsequent excavators such as Bliss and Dickie, Johns and Kathleen Kenyon. A large section below Robinson’s Arch was cleared during Benjamin Mazar’s excavations in the 1970’s. Not only did Warren publish a plan of the tunnel, but in the 1970’s the Irish architect David Sheehan together with my late sister Martha made a detailed survey of the tunnel. The tunnel was constructed as a drain below the street that ran above it.
This plan is based on Warren’s drawing and is published in my book The Quest, p. 56:

There are two distinct phases to be discerned in the tunnel. The older sections to the north and to the south on the plan are roofed with flat slabs, while the central section has a vaulted roof. The flat roofed sections used to belong to one and the same Pre-Herodian, possibly Hasmonean period, while the vaulted section is Herodian.

It is clear from the above plan that the construction of the Herodian southwest corner of the Temple Mount cut the earlier drain and a detour was constructed going round this corner, using short sections of vaulting, to reconnect the drain again. This Herodian section also cut through some First Temple period tombs:

Even Israeli commentators don’t get the purpose of this tunnel right. According to this report:
Visitors are now able to walk from the center of Silwan to the Western Wall plaza within several minutes, via a shaft that researchers believe was used for drawing water from the tunnel. The shaft is in the area of the Davidson Archaeological Park and Center, between the southern wall of the Temple Mount and the Dung Gate, and when the work is completed it will serve as the entrance to the tunnel.
The purpose of this tunnel was not to supply water, but to drain away rainwater that fell on the street and to drain off the sewage of adjacent buildings into the drain:

During the Mazar excavations, this tunnel was visited many times by staff and volunteers alike. It is great to hear that the full length of this drain has been opened all the way down to the Siloam Pool. It will be exciting to walk again through this tunnel, but while doing so, one should also remember that in 70 AD many Jerusalemites tried to escape through this same tunnel, but were cruelly killed by the Romans when they were discovered.