The Stepped Stone Structure is the name given to the remains at a particular archaeological site (sometimes termed Area G) on the eastern side of the City of David, the oldest part of Jerusalem. The curved, 60ft high, narrow stone structure is built over a series of terraces (hence the name). A casemate wall adjoins the structure from a northerly direction at the upper levels, and may have been the original city wall.
It was uncovered during a series of excavations by R.A.S. Macalister in the 1920s, Kathleen Kenyon in the 1960s, and Yigal Shiloh in the 1970s-80s. Kathleen Kenyon dated the structure to the start of Iron Age II (1000-900 BC); Macalister believed it to be Jebusite. Macalister, the first to excavate the structure, called the remains he had found a ramp; other scholars, after the more recent discoveries by Kenyon and Shiloh, have suggested that it might be a retaining wall, or a fortress. Israel Finkelstein et al.suggest that the upper part of the structure was substantially rebuilt in the Hasmonean period.
It is hypothesized that the structure may be the Biblical Millo. A recent excavation by Eilat Mazar directly above the Stepped Stone Structure shows that the structure connects with and supports the Large Stone Structure. Mazar presents evidence that the Large Stone Structure was an Israelite royal palace in continuous use from the tenth century until 586 BCE. Her conclusion that the stepped stone structure and the large stone structure are parts of a single, massive royal palace can be viewed in the light of the biblical reference to the House of Millo in II Kings 12:21 and II Chronicles 24:25 as the place where King Joash was assassinated in 799 BCE while he slept in his bed. Millo is derived from "fill", (Hebrew milui). The stepped stone support structure is built of fills.