In 2 Kings 20:20, it says: “As for the other events of Hezekiah's reign, all his achievements and how he made the pool and the tunnel by which he brought water into the city, are they not written in the book of the annals of the kings of Judah.”
The Siloam inscription, found in 1880 beneath the old city of Jerusalem in an underground water conduit, was written in Old Hebrew and dates to 702 B.C. It shows that Hezekiah ordered the construction of the tunnel and provides details of its engineering. Beginning at opposite ends, the workers chiseled the tunnel out of solid limestone until they met in the middle.
Hezekiah's tunnel is about a third of a mile long and less than three feet wide. In some places it is less than five feet high. Beginning at the Gihon Spring, outside Jerusalem, the tunnel ran beneath a hill and under the city wall to the Siloam Pool.
Hezekiah built the tunnel as a defense against the imminent siege of Sennacherib, ruler of the Assyrians, which happened in 701 B.C. (2 Chronicles 32:2–4, 30). The Prism of Sennacherib, housed in the University of Chicago Oriental Institute, provides an account of Sennacherib's siege of Jerusalem.
The Bible says that the Assyrian king Sennacherib captured Judah's fortified cities, including Lachish, during the reign of King Hezekiah. The Assyrian king demanded a tribute from King Hezekiah that included “all the silver that was found in the temple of the Lord and in the treasuries of the royal palace” (2 Kings 18:13–17). Sennacherib's campaign against Judah is recorded on the Prism of Sennacherib and on the Lachish reliefs. Second Kings 19:37 says that Sennacherib was assassinated by two of his sons, Adrammlech and Sharezer. This is shown in the annals of a third son, Esarhaddon, who succeeded his murdered father as king.