The Millo (Hebrew: המלוא) was a structure in Jerusalem first mentioned in the book of 2 Samuel 5:9 and corresponding passages in the Books of Chronicles and the Books of Kings. However it is mentioned as being part of the city of David and seems to have been a rampart built by the Jebusites prior to Jerusalem's being conquered by the Israelites. The texts also describe a Millo built by Solomon and repaired by Hezekiah, without giving an explanation of what exactly the Millo was. There is some debate among scholars as to the Millo's specific nature. The most common assumption among archaeologists and historians of ancient Israel is that the Millo is the Stepped Stone Structure uncovered by Kathleen Kenyon and demonstrated by Eilat Mazar to be connected to the recently uncovered Large Stone Structure.
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 BC. Her conclusion that the stepped stone structure and the large stone structure are parts of a single, massive royal palace makes sense of the biblical reference to the millo as the House of Millo in II Kings 12:21 and II Chronicles 24:25 as the place where King Joash was assassinated in 799 BC while he slept in his bed. Millo is derived from "fill," (Hebrew milui). The stepped stone support structure is built of fills.
In the Book of Samuel, Millo is mentioned as the boundary of King David's construction while building up the City of David after the capture of Jerusalem from the Jebusites. The King James Version (translation into English) footnotes Millo as literally, "The Landfill," while the New International Version translates it to "supporting terraces."