Herod the Great enlarged the Temple Mount in Jerusalem during the late first century BCE and early first century CE. He built a much larger rectangular platform, supported by massive retaining walls; the Western Wall is one side of that platform, not a surviving wall of the Temple building itself.
What the wall supported
The enclosure created a broad, level precinct around the Second Temple. The western retaining wall includes monumental limestone blocks laid in courses. Its visible section is only part of the full western side, much of which runs below the modern city and can be seen in sections through the Western Wall Tunnels.
Excavations by the Israel Antiquities Authority identified a long cast wall with drainage channels and vaulted tunnels near the confluence of the Tyropoeon and Transversal valleys. The excavators date it to Herod’s era and interpret it as part of the area’s layout and water management before the Temple Mount expansion. A paved road apparently ran above it toward a gate in an earlier enclosure. The IAA excavation report describes these successive construction phases.
Streets, arches and tunnels
Herod’s project connected the elevated precinct to Jerusalem’s lower streets. At the southwest corner, a monumental arch carried a road toward the Temple Mount; the remains are known as Robinson’s Arch. Nearby excavations exposed a paved street and a large drainage channel. The IAA’s Robinson’s Arch report documents the street-level remains and the channel cut beside the enclosure.
The tunnels open views of buried portions of the retaining wall and the city built beside it. They do not expose the entire 488-meter western side. Recent excavations in the tunnel complex have also found a Herodian-period dam wall, water channels and a later stone-paved building with a fountain and dining halls. The Israel Antiquities Authority’s 2025 study dates the dam wall to the latter half of the first century BCE and describes later reuse.
These remains show how the Temple precinct was engineered into Jerusalem’s terrain and linked to its streets and water systems. For the Wall’s role in Jewish prayer, see why Jews pray at the Western Wall.