A stronghold at Shechem (Judges 9:6,20) and a fortification in Jerusalem (2 Samuel 5:9; 1 Kings 9:15). The name derives from millo (H4407), meaning a filling or rampart — a section of wall filled with earth and stone for defensive strength.
Beth-Millo at Shechem was the seat of power for Abimelech's failed kingship — a cautionary tale about usurped authority and the dangers of charismatic leadership without divine sanction. The Millo in Jerusalem, however, was part of David's royal city-building and Solomon's fortification program — legitimate kingdom construction under God's covenant. The contrast teaches that the same architectural feature (a filling/rampart) can represent either corrupt human ambition or faithful covenant stewardship, depending on the heart that drives the builder.