The Biblical account of this king is contained in 2 Kings 18:20, Isaiah 36-39, and 2 Chronicles 29-32. These sources portray him as a great and good king, following the example of his great-grandfather Uzziah. He set himself to abolish idolatry from his kingdom, and among other things which he did for this end, he destroyed the "brazen serpent," which had been relocated at Jerusalem, and had become an object of idolatrous worship. A great reformation was wrought in the kingdom of Judah in his day (2 Kings 18:4; 2 Chronicles 29:3-36). The author of 2 Kings ends his account of Hezekiah with praise (18:5).
Between the death of Sargon, and the succession of his son Sennacherib, Hezekiah sought to throw off his dependence to the Assyrian kings. He refused to pay the tribute enforced on his father, and "rebelled against the king of Assyria, and served him not," but entered into a league with Egypt (Isaiah 30; 31; 36:6-9). This led to the invasion of Judah by Sennacherib (2 Kings 18:13-16) in the 4th year of Sennacherib (701 BC). Hezekiah anticipated the Assyrian invasion, and made at least one major preparation: in an impressive engineering feat, a tunnel 533 meters long was dug in order to provide Jerusalem underground access to the waters of the Spring of Gihon, which lay outside the city. (The work is dscribed in the Siloam Inscription, which has been dated to his reign on the basis of its script.) At the same time, a wall was built around the Siloam Pool, into which the waters from the spring flowed (Isaiah 22:11). An impressive vestige of this structure is the broad wall in the Jewish Quarter of the Old City of Jerusalem.
"When Hezekiah saw that Sennacherib had come, intent on making war against Jerusalem, he consulted with his officers and warriors about stopping the flow of the springs outside the city . . . for otherwise, they thought, the King of Assyria would come and find water in abundance" (2 Chronicles 32:2-4). Sennacherib records on his monumental inscription, "The Prism of Sennacherib", how in his campaign against Hezekiah ("Ha-za-qi-(i)a-ú") he took forty cities in this campaign, and besieged Jerusalem ("Ur-sa-li-im-mu") with earthworks. Eventually Hezekiah saw Sennacherib's determination, and offered to pay him three hundred talents of silver and thirty of gold in tribute, despoiling the Temple to produce the promised amount (18:14-16).
The narrative in the Bible states Sennacherib invaded Judah again within two years (Isaiah 33:1; 2 Kings 18:17; 2 Chronicles 32:9; Isaiah 36). According to the Biblical accounts, this invasion ended in the destruction of Sennacherib's army, when Hezekiah prayed to God and "that night the angel of the Lord went out, and smote in the camp of the Assyrians 185,000 men." The author of the Books of Kings remembers to include the fact that (19:37), seventeen years later, Sennacherib was assassinated by his sons Adrammelech and Sharezer, and Esarhaddon became the Assyrian king. There is also a less miraculous account from the Assyrian side of that Sennacherib's raised his siege of Jerusalem after Hezekiah acknowledged Sennacherib as his overlord and paid him tribute.
The narrative of Hezekiah's sickness and miraculous recovery is found in 2 Kings 20:1, 2 Chronicles 32:24, Isaiah 38:1. Various ambassadors came to congratulate him on his recovery, among them Merodach-baladan, the king of Babylon (2 Chronicles 32:23; 2 Kings 20:12).
There is considerable uncertainty about the actual dates of his reign. First, the Biblical records are conflicting, as they are for a number of rulers of Israel and Judah. 2 Kings 18:10 dates the fall of Samaria to the sixth year of Hezekiah's reign, which would make 728 BC the year of his accession. However, verse 13 of the same chapter states that Sennacherib invaded Judah in the fourteenth year of Hezekiah; the Assyrian records leave no doubt that this invasion took place in 701 BC, which would fix 715 BC as Hezekiah's initial year, which would be confirmed by the account of his illness. In chapter 18 of 2 Kings book it is stated that during the 14th year of his reign, Sennacherib had returned to pillage Samaria, setting up his base of operations at Lachish and threatening Jerusalem, forcing Hezekiah to pay tribute. As the description in chapter 20 of Hezekiah's illness immediately follows Sennacherib's departure, this would date his illness to his 14th year, which is confirmed by Isaiah's statement that he will live fifteen more years (29-15=14). His fourteenth year being 701 BC, the first must have been 715 BC.
Another set of calculations show it is probable that Hezekiah did not ascend the throne before 722 BC. By W.F. Albright's calculations, Jehu's initial year is 842 BC; and between it and Samaria's destruction the books of Kings give the total number of the years the kings of Israel ruled as 143 7/12, while for the kings of Judah the number is 165. This discrepancy, amounting in the case of Judah to 45 years (165-120), has been accounted for in various ways; but every one of those theories must allow that Hezekiah's first six years as well as Ahaz's last two fell before 722 BC. Nor is it clearly known how old Hezekiah was when called to the throne,although 2 Kings 18:2 states he was twenty-five years of age. His father (2 Kings 16:2) died at the age of thirty-six; it is not likely that Ahaz at the age of eleven should have had a son. Hezekiah's own son Manasseh ascended the throne twenty-nine years later, at the age of twelve. This places his birth in the seventeenth year of his father's reign, or gives Hezekiah's age as forty-two, if he was twenty-five at his accession. It is more probable that Ahaz was twenty-one or twenty-five when Hezekiah was born (and suggesting an error in the text), and that the latter was thirty-two at the birth of his son and successor, Manasseh.
Still another date is possible by astronomical calculations. 2 Kings 20:8-11 speaks obscurely about "the shadow" moving "ten degrees" during the above mentioned illness of Hezekiah (as does Isaiah 38:7f). Professor Aurel Ponori-Thewrewk, retired director of the planetarium of Budapest, Hungary, may have been the first scholar to offer an astronomical explanation this passage; observing that new Bible translations use "the sundial of Ahaz," while other Bibles "the stairway of Ahaz," he states that the original Hebrew text says ma(c)alóth, the plural of ma(c)alah. Therefore, his conclusion is that it had a double meaning: while it refers to the steps over which the shadow has already passed, it may have meant the instrument (?) of Ahaz which had obviously contained more than ten units, and on which Hezekiah could observe the movement of the sun's shadow. But whatever has been the original meaning of the Hebrew word, Ponori-Thewrewk says, the shadow had made an abnormal movement on it. He imagines a pole or gnomon that casts a shadow on a plane that is perpendicular to it. The shadow can move ahead for a while, then it can move backward on that plane.
John D. Davis, Davis dictionary of the Bible (Baker Book House, 1975: 184) confirms the possibility that 2 Kings 20:11 and Isaiah 38:8 may be explained by a solar eclipse, and the stairway of Ahaz may have been a sundial with a projecting gnomon to cast a shadow. The foretold backward position of the sun's shadow, could have been caused by an eclipse of the sun, probably on May 6, 724 BCE. This eclipse took place between 6:09 and 8:24 a.m., its maximum was 64.3% at 7:15 a.m. This would then date Hezekiah's first year as king to 738 BC, and his last to 709 BC. It is possible that Isaiah (38: 7-8) had been informed beforehand by an astronomer, perhaps by one of Merodach-baladan's envoys, about the expected date of a solar eclipse on May 6, so Isaiah conforted the king on May 3.