A seal from the days of the First Temple has been discovered below the southwestern corner of the Temple Mount. From the press release by the Israel Antiquities Authority:

The remains of a building dating to the end of the First Temple period were discovered below the base of the ancient drainage channel that is currently being exposed in IAA excavations beneath Robinson’s Arch in the Jerusalem Archaeological Garden, adjacent to the Western Wall of the Temple Mount. This building is the closest structure to the First Temple found to date in archaeological excavations.
In the excavations, underwritten by the Ir David Foundation, a personal Hebrew seal from the end of the First Temple period was discovered on the floor of the ancient building. The seal is made of a semi-precious stone and is engraved with the name of its owner: “Lematanyahu Ben Ho…” (“למתניהו בן הו…” meaning: “Belonging to Matanyahu Ben Ho…”). The rest of the inscription is erased.

Two people with the name Mattaniah are mentioned in 1 Chronicles 25:4, 16 and 2 Chronicles 29:13.

The full press release is here. Leen Ritmeyer comments on the location of the find. Joseph Lauer passes on word that some information in the press release is incorrect. According to Zachi Dvira (Zweig), “This was not sifted at our site. And the visitors sift only the debris from the Temple Mount.

Only our staff workers do the sifting for other excavations.”