Jerusalem’s Newly Discovered Siloam Dam Confirms Biblical Engineering from Joash to Jesus

Jonathan Moore, D.P.M., Ph.D.

Inspiration of the BibleArchaeologyIn the News

Under the very pool where Jesus healed a man born blind, archaeologists have uncovered the largest dam ever found in ancient Israel—a monumental wall more than 40 feet high that predates the Pool of Siloam by nearly eight centuries. This new discovery, announced in 2025 by a joint team from the Israel Antiquities Authority and the Weizmann Institute of Science, connects the faith of the Gospel accounts with the royal engineering of Judah’s earliest kings. Far from myth or legend, the evidence emerging from Jerusalem’s bedrock powerfully validates the biblical record, linking King Joash1 to the later waterworks of King Hezekiah and the very pool where the Savior restored sight to the blind.

1. The Pool of Siloam in the Time of Jesus (1st Century A.D.)

In John 9:1-11, the Gospel writer recounts how the Lord Jesus anointed the eyes of a blind man with clay and told him to “Go, wash in the Pool of Siloam.” For centuries, the pool’s exact location was uncertain. Many assumed it was the small Byzantine basin near the Church of St. Saviour until 2004, when workers repairing a water pipe in the southern City of David uncovered stone steps descending into a vast plastered pool. Archaeologists Ronny Reich and Eli Shukron soon identified this as the authentic Second-Temple Pool of Siloam, the very site referenced in the New Testament.2

The stepped pool—roughly 225 feet long and 15 feet deep—was constructed during the reign of Herod the Great in the late first century B.C., at the height of Jerusalem’s expansion.3 Fed by the ancient Siloam Tunnel, the pool collected water from the Gihon Spring and served both as a public reservoir and as a massive mikveh (ritual bath) for pilgrims ascending the Pilgrimage Road toward the Temple Mount.4 Its architectural grandeur reflects Herod’s vast building program, which included the Temple complex itself. When Jesus performed His miracle there, He stood amid a system that had already been serving God’s people for over seven centuries—a line of hydraulic continuity stretching back to the time of Judah’s earliest kings.

2. Hezekiah’s Tunnel: Engineering Under Siege (Late 8th Century B.C.)

Long before Herod’s reconstruction, the same spring that fed the Siloam Pool had already been secured by one of the Bible’s most famous engineers: King Hezekiah. Facing the Assyrian invasion in 701 B.C., Hezekiah ordered the diversion of Jerusalem’s water supply into the fortified city. As 2 Kings 20:20 records, “He made the pool and the conduit and brought water into the city.” Archaeology confirms this in the Siloam Tunnel, an underground passage roughly 1,750 feet long that connects the Gihon Spring on the east to the lower valley on the west.5

Cut through bedrock, the tunnel winds in an S-shaped path and terminates near the location of the later Herodian pool. Its ancient Hebrew inscription—carved near the southern exit—commemorates the meeting of the two work crews who tunneled toward one another.6 The engineering precision required to complete such a project testifies to the royal resources and administrative capacity of Hezekiah’s reign.

By channeling water inside Jerusalem’s walls, Hezekiah effectively replaced an earlier open reservoir, transforming an external valley dam into a protected, internal water source. His system not only supplied the city during siege but also paved the way for the later Herodian expansions that pilgrims of Jesus’ day would see.

3. The Newly Discovered Siloam Dam of King Joash (Early 8th Century B.C.)

Beneath these familiar works lies an even older foundation. In 2025, Johanna Regev, Nahshon Szanton, Filip Vukosavović, Itamar Berko, Yosef Shalev, Joe Uziel, and Elisabetta Boaretto published the results of their radiocarbon analysis of mortar samples from a massive stone wall at the southern mouth of the Tyropoeon Valley.7 The results—calibrated to between 805 and 795 B.C.—place the wall firmly within the reign of King Joash (r. ca. 835-796 B.C.).8

The wall, more than 40 feet high and 26 feet thick, sealed the valley and impounded both runoff and overflow from the Gihon Spring, forming an enormous open reservoir—the earliest known Pool of Siloam. Excavations revealed that this dam and its reservoir lay within the southern extent of ancient Jerusalem, inside what became the lower City of David. By Hezekiah’s time, the area was fully fortified, ensuring that the reservoir stood within the city’s defensive walls, precisely where the later Herodian pool would be expanded in the first century B.C. This confirms a continuous chain of hydraulic development at the same site—from Joash’s dam to Hezekiah’s tunnel to Herod’s monumental pool.9

Radiocarbon dating of embedded twigs and straw produced a tight 10-year range, while paleo-climatic data from Dead Sea cores and Soreq Cave stalagmites confirmed that Jerusalem faced alternating drought and flash floods during this era. The construction of such a dam provided both flood control and long-term water storage, demonstrating advanced planning under royal oversight. In every sense, the Joash dam anticipates the later biblical account of Hezekiah’s engineering reforms.

Its discovery vindicates the biblical portrayal of Judah’s early monarchy as organized, literate, and technologically capable—precisely the kind of kingdom that could undertake monumental civic works consistent with the historical books of 2 Kings and 2 Chronicles.

4. Canaanite Foundations: Jebus, the Water Systems Before Israel

Long before Israelite kings ruled Jerusalem, the Canaanite city of Jebus—the stronghold later conquered by King David (2 Samuel 5:6-9)—had already fortified the Gihon Spring with towers, tunnels, and a rock-cut pool inside its wall. Excavations by Kathleen Kenyon in the 1960s and Ronny Reich and Eli Shukron in the 1990s revealed a monumental Spring Tower—a defensive structure enclosing access to the spring from within the city.10 This earliest water system included a stepped tunnel descending to a protected pool, ensuring access to water during siege. Although the Bronze-Age pool differs in scale and purpose from the later Siloam installations, it set the hydraulic pattern that successive builders—Joash, Hezekiah, and finally Herod—would each adapt for their generation.11

Moreover, the biblical book of Genesis identifies the city as Salem when Melchizedek is called “king of Salem” (Genesis 14:18-20), and Psalm 76:2 equates Salem with Zion, reinforcing the view that Jerusalem’s geographical identity stretches back into the early patriarchal period.

5. Continuity and Theological Significance

From the Bronze-Age foundations to the Herodian expansion, the Pool of Siloam embodies the continuity of Divine provision in Jerusalem’s history. Through every era, God’s people found both physical and spiritual refreshment in the same flowing waters of the Gihon Spring. Isaiah warned those who “refused the waters of Shiloah that flow gently” (Isaiah 8:6), while later prophets spoke of “drawing water from the wells of salvation” (Isaiah 12:3). Hezekiah’s tunnel fulfilled this prophecy in physical form—securing the city’s lifeline amid peril.

Centuries later, Jesus transformed that physical image into spiritual truth: “If anyone thirsts, let him come to Me and drink” (John 7:37). The Siloam Pool thus stands as both a technological marvel and a living parable of redemption. The recent discovery of the Joash-era dam reinforces that Scripture’s record of royal infrastructure was not theological metaphor but historical reality—its stones still bearing witness to the ingenuity and faith of ancient Judah.

Conclusion

The unveiling of the Siloam Dam beneath Jerusalem’s City of David represents one of the most significant discoveries in decades—an engineering bridge linking Joash, Hezekiah, Herod, and Jesus. Each generation modified the same life-giving spring: Joash contained it with a massive dam; Hezekiah redirected it with a tunnel; Herod adorned it with stone steps; and Jesus sanctified it with a miracle.

Modern science has now dated the earliest phase of this system with remarkable precision, confirming that Judah’s kings were capable of large-scale, organized public works as the Bible describes. The stones cry out in testimony that the biblical narrative stands—not on myth—but on measurable history. In the Pool of Siloam—past and present—the waters still proclaim the truth of God’s Word: “With joy you will draw water from the wells of salvation” (Isaiah 12:3).

[Dr. Jonathan Moore—Field Archaeologist with the Shiloh Excavation, Israel; Adjunct Faculty at Freed-Hardeman University; and Founder of Seeing His World, a missions-based educational nonprofit dedicated to providing academically grounded yet spiritually transformative guided experiences throughout the Bible lands (www.seeinghisworld.com).]

Endnotes

1 King Joash (Jehoash) reigned in Judah ca. 835-796 B.C. following a period of protection and oversight by Jehoiada the priest (see 2 Kings 11-12; 2 Chronicles 24). Crowned at age seven, he initially “did what was right in the eyes of the LORD” under Jehoiada’s guidance but later turned from faithfulness, permitting idolatry and ordering the death of the prophet Zechariah (2 Chronicles 24:20-22). He was assassinated by his servants and succeeded by his son Amaziah.

2 Ronny Reich and Eli Shukron (2005), “The Second-Temple Period Pool of Siloam in Jerusalem,” Israel Exploration Journal, 55:153-167.

3 “The Siloam Pool: Where Jesus Healed the Blind Man,” Biblical Archaeology Society, www.biblicalarchaeology.org/daily/biblical-sites-places/biblical-archaeology-sites/the-siloam-pool-where-jesus-healed-the-blind-man/.

4 Nahshon Szanton and Joe Uziel (2019), “The Pilgrimage Road: Jerusalem’s Ascent from the Pool of Siloam to the Temple,” City of David Studies.

5 Dan Gill (1983), “The Siloam Tunnel Reconsidered,” Nature 305:515-517.

6 James B. Pritchard (1969), Ancient Near Eastern Texts Relating to the Old Testament (Princeton University

7 Johanna Regev, et al. (2025), “Radiocarbon Dating of Jerusalem’s Siloam Dam Links Climate Data and Major Waterworks,” Proceedings of the National Academy of Sciences of the United States of America, 122[35], https://doi.org/10.1073/pnas.2510396122.

8 Note that radiocarbon dating does, in fact, sometimes result in ages of materials that exceed 10,000 years. Radiocarbon dating, however, is understood to be suspect for objects thought to be older than roughly 3,000-4,000 years old [cf. George H. Michaels and Brian Fagan (2013), “Chronological Methods 8—Radiocarbon Dating,” University of California Santa Barbara Instructional Development.]. Further, biblical creationists argue that radioactive decay rates were apparently accelerated during the Flood and afterward, possibly up to 1,500-1,000 B.C., making all dating techniques unreliable for ages beyond that time. For evidence of accelerated radioactive decay in the past, see Don DeYoung (2008), Thousands…Not Billions (Green Forest, AR: Master Books).

9 City of David Foundation (2025), “Monumental Dam from the Time of Biblical Kings Uncovered,” August 29.

10 Kathleen M. Kenyon (1967), Jerusalem: Excavating 2000 Years of History (New York: McGraw-Hill), pp. 31-45.

11 See “Salem (Bible),” Wikipedia, en.wikipedia.org/wiki/Salem_(Bible) (accessed September 2025); Armstrong Institute, “The Incredible Origins of Ancient Jerusalem,” armstronginstitute.org/843-the-incredible-origins-of-ancient-jerusalem/ (accessed September 2025).

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