The Siloam Tunnel inscription dates to around 700 BCE during the reign of Hezekiah. The date is based on paleographical analysis of the inscription which shows features typical of 8th century BCE Hebrew. The inscription seems to commemorate the completion of the Siloam Tunnel connecting the Gihon spring to the pool of Siloam inside Jerusalem, a public work attributed to King Hezekiah in 2 Chronicles 32:30 and necessitated by the Assyrians’ impending siege.
2 Chr 32:30 This same Hezekiah closed the upper outlet of the waters of Gihon and directed them down to the west side of the city of David. And Hezekiah prospered in all his works.The language is very similar to biblical Hebrew, and the spelling (orthography) fits the late 8th century with final but not internal matres (vowel letters). It was found on the wall of the tunnel in 1880.
[הנקבה וזה היה דבר הנקבה בעוד [ההצבם מניפם את
הגרזן אש אל רעו ובעוד שלש אמות להנקבה נשמע קל אש ק
רא אל רעו כי היתה זדה בצר מימני . . . ובים ה
נקבה הכו החצבם אש לקרת רעו גרזן על גרזן וילכו
המים מן המוצא אל הברכה במאתים ואלף אמה ומא
ת אמה היה גבה הצר על ראש החצבםTranslation
(1) The breach. And this was the record of the breach. While [the workmen were swinging,] (2) the pick-axe, each man toward his companion, and while there were three cubits to be tunneled, a voice was heard- each man called (3) to his companion because there was a crack in the rock from the right…and on the day of (4) the breach the workers struck, each man to meet his companion, pick-axe against pick-axe. And the waters flowed (5) from the source to the pool: one thousand and two hundred cubit[s]. And one hundred (6) cubit[s] was the height of the rock over the head of the workmen.Reference: The line drawing above is from J. Renz and W. Rollig, Handbuch der altehebraischen Epigraphik, Wissenschaftliche Buchgesellschaft, 1995.
1 This dating was famously (and foolishly) challenged by J. Rogerson and P. R. Davies (“Was the Siloam Tunnel Built by Hezekiah?” Biblical Archaeologist 59:3 (1993), 138-149) who argued the inscription was Hasmonean. An international dream team of paleographers and philologists (including Jo Ann Hackett, Frank Moore Cross, P. Kyle McCarter, Jr., Ada Yardeni, André Lemaire, Esther Eshel, and Avi Hurvitz) administered a massive smackdown in the pages of BAR a few years later (“Defusing Pseudo-Scholarship: The Siloam Inscription Ain't Hasmonean.” BAR (Mar/Apr 1997), 41-68).