Sennacherib's attack was not a surprise; Hezekiah provoked it by breaking a treaty (2 Kings 18:7, 20). Water was crucial for both attackers and defenders during sieges. Hezekiah ensured Sennacherib's army could not access the city's water supply. In a famous ancient engineering feat, Hezekiah's tunnel connected the fresh waters of the Gihon Spring to the Pool of Siloam, providing water within the city walls. This tunnel is almost 530 meters long (about 580 yards or one-third of a mile) and about two meters (six feet) high. The Hezekiah inscription, found in the tunnel in 1880, describes how the excavators met to connect the two ends. Although much of the tunnel used natural underground aqueducts, it was a brilliant strategy to protect the city's citizens.